Camp Ondessonk is an outdoor, Catholic residential youth camp run by the Diocese of Belleville. It is located in the Shawnee National Forest of Southern Illinois, near Ozark, Illinois. The mission of the camp is "Exceptional outdoor and spiritual adventures empowering kids of all ages." Camp Ondessonk is accredited by the American Camp Association.

Camp Ondessonk started as a summer program in 1957. Known as Camp St. Philip, the program is part of the Diocese of Belleville. Having no facilities of their own, camp administrators rented out Camp Piasa in Grafton, Illinois in 1957 and Camp Vandeventer in Waterloo, Illinois in 1958. Each summer, the camps were staffed by seminarians and college students all under the direction of Monsignor John T. Fournie.

Camp St. Philip offered participants outdoor activities such as riflery, archery, swimming, and handicrafts, as well as other activities such as cooking, housekeeping, and axmanship. The camp also offered a camping honor society. Campers at St. Philip spent their nights in one of five units; Marquette, LaSalle, Lalande, Brebeuf, and Hennepin.

Led by a desire for a permanent location for a Catholic youth camp, Monsignor Robert DeGasperi oversaw the effort to gain leases of the land that would become Camp Ondessonk. Volunteer crews began construction at the current site in the spring of 1959. 481 campers and 52 staff attended over a four-week period that the camp was open. Campers were grouped into four units – Brebeuf, Chabanel, Goupil, and LaLande. Activities included swimming, archery, riflery, horseback riding, nature hikes, and camp crafts.

In the 1960s, additional camping weeks were added to the schedule because of demand. More space was added with the construction of more units - Daniel, Garnier, Tekakwith, Amantacha, Ahatsistari and Lalemant. Some units were tents while others were cabins. An adventure program was based in the unit of Teondecoren. The swimming lake – Lake St. Isaac – was added as well as Lake Echon, a separate lake for watercraft. A bridge was built over Lake Echon and was dedicated to the memory of Larry Garner, a former staff member who was killed in action in Vietnam. Awards in the form of arrowhead-shaped patches were added for skills mastery for the various activities. Pioneer sessions were introduced in 1965 to give campers a more in-depth experience through a two week program. The Pioneer Sessions led to the formation of Frontier Units in the 1970s. Although they were referred to as units, the Frontier program was a separate experience from camp, during which participants traveled to places offsite.

In the late 1970s the Silver and Golden Frontier Program was added. Inspired by the original Frontier units, the Silver and Golden Frontier trips catered to adults wishing to travel around the country.

To help with the expanding interest, Ahatsistari and Lalemant were built as cabins in order to accommodate more campers. The camp program was expanded to include an all-day exploration to give the campers the chance to explore the land around them. A marathon competition was added as well. The Garnier tree houses were built up shore from the original cabins and the Amantacha bridge was added to replace the various methods of getting campers across Lake Echon. Chabanel was moved to its current location in 1979.

The Lalande cabins were rebuilt into tree houses in 1981. Other units were rebuilt in this period as well. A new barn was added in 1983 and a new health center was added in 1986. By 1989 the units of Teondecoren and Ahatsistari were no longer available to campers as a unit choice. Coed sessions were added in 1989.

Specialty Camps were introduced in the summer of 1992. In 1995, Teondecoren was reintroduced as a tepee unit for one summer. In 1996, the camp was accredited by the American Camping Association (later renamed the American Camp Association). A minicamp program was introduced for younger campers in 1999.

Camp Ondessonk was also accredited by the Certified Horsemanship Association in 2003. A new dining hall was opened for the summer of 2004.

Camp Ondessonk acquired an American Black Bear named Tommy 1966 from Omar's Bikini Club near East St. Louis. Tommy lived at the camp for 28 years.

The camp acquired another bear in 1995 and named him Yonah. "Yona" in Cherokee means "bear." Yonah lived at the camp until his death in 2001.

The symbol of Camp Ondessonk is a circle with a cross coming out of the top and seven stars surrounding it representing the eight North American Martyrs. The circle represents an ‘O’ for Ondessonk, a name given to one of the eight martyrs, St. Issac Jogues, and it also represents the world.

The other seven martyrs are represented with stars on the camp's symbol. The two stars on the top left represent St. Jean de Brébeuf and St. Gabriel Lalemant. The star on the top right represents St. Jean de Lalande. The four remaining martyrs and represented with stars on the bottom right, St. René Goupil, St. Antoine Daniel, St. Noël Chabanel, and St. Charles Garnier.

The cross represents a world dedicated to Christ. It also serves as a reminder of Camp Ondessonk's mission as a Catholic camp for children.

The name "Ondessonk" is the Huron word for "Bird of Prey." It is the name that the Huron gave to St. Issac Jogues when he was serving among them as a Jesuit missionary, because of his black robe. Jogues came to this country from France in the early 17th century in an effort to bring the Gospel to the American Indians. He ended up giving his life to this task when he was tortured and later martyred.

Several Jesuit missionaries were martyred while working among the Huron and Iroquois people. These saints and their American Indian companions are honored and remembered at Camp Ondessonk with the camp units, lakes, and major land forms named after them. The lives of the martyrs and other namesakes of the camp serve as an inspiration for Christian living. The North American Martyrs are:

• St. Isaac Jogues - priest, served as a missionary among the Hurons and Iroquois nations. Succeeded Jérôme Lalement, uncle of Gabriel Lalemant, as Superior of the Ihonatiria mission founded by Brébeuf. Jogues witnessed the death of René Goupil.
• St. Jean de Brébeuf - priest, served in New France for about 18 years, founding a mission at Ihonatiria and served as the Superior of that mission.
• St. Noël Chabanel - priest, not as gifted with languages as other missionaries, Chabanel was at the Saint-Jean mission among the Tobacco Indians in 1649 when he received orders to go to the main residence, Sainte-Marie II, on the Île Saint-Joseph. He set out on December 7 and was slain by a Huron apostate according to accounts written by Paul Ragueneau.
• St. Antoine Daniel - priest, assigned with Brébeuf to the Huron mission, Daniel was very gifted with learning the languages of his surroundings. Daniel was the first of the Jesuit missionaries to be martyred in Huronia. The Hurons had given Daniel the name of Anȣennen.
• St. Charles Garnier - priest, called Ouracha by the American Indians, Garnier traveled with Pierre Chastellain to the Huron territory. While not very successful in his initial missionary work, Garnier established a new mission in the fall of 1646 that had much success. Garnier was martyred at this mission in December of 1649.
• St. Gabriel Lalemant - priest, served with Brébeuf when the village they were in was captured by Iroquois. Both priests were martyred about a day apart from each other.
• St. René Goupil - layman, Goupil was traveling with Isaac Jogues, Guillaume Couture, Eustache Ahatsistari and Joseph Teondechoren, and the latter’s niece, daughter of Joseph Chiwatenhwa, Thérèse Oionhaton, when he was captured by the Iroquois. Days after taking vows before Jogues as a lay brother in the Society of Jesus, Goupil was martyred for making the sign of the cross on a child's head while in captivity near Auriesville, New York. He was the first of the eight North American Martyrs to receive the crown of martyrdom and the first canonized Catholic martyr in North America.
• St. Jean de Lalande - layman, Lalande traveled with Jogues to Iroquois country to negotiate peace among the nations in that region. Both men were treated as enemies by the Iroquois and martyred near Auriesville, New York.

The feast day for the North American Martyrs is celebrated as a Memorial on October 19 for the United States. In Canada, the North American Martyrs is celebrated as a Feast on September 26.

• Amantacha, baptized as Louis de Sainte-Foi, was a Huron educated in France possibly under the instruction of Antoine Daniel. He later became a friend and aide of the Jesuit missionaries. Amantacha was captured in a raid and believed to have been killed by his captors.
• Paul Ragueneau, priest, a Jesuit missionary who was a part of the Huron mission and worked under the instruction of Jean de Brébeuf and Jérôme Lalemant (uncle to the martyr Gabriel Lalemant) for eight years. Ragueneau documented much of the history that we have today of the North American Martyrs, even proposing the cause for canonization for the North American Martyrs. The unit of Raganeau uses a slightly different spelling of his name.
• St. Kateri Tekakwitha, originally known as Catherine Tekakwitha and known as Lily of the Mohawks was an Algonquin and Iroquois Native American woman from New France and an early convert to Roman Catholicism. She was recognized as the first Native American saint in 2012. Her feast day is July 14.
• Joseph Chiwatenhwa was one of the first Native Americans to respond to the Gospel. Having met Brébeuf, Chiwatenhwa learned about the Christian faith. In 1637, a year after Chiwatenhwa's first encounter with Jesuits, Chiwatenhwa's wife, Aonetta, gave birth to a baby boy who was baptized by the Jesuit missionaries. Chiwatnenhwa later contracted a fever and was baptized on August 16, 1637, taking the name Joseph. Chiwatenhwa is known as "the forgotten martyr" or "the first Huron martyr."
• Marie Aonetta was baptized on March 19, 1638 and married Joseph Chiwatenhwa immediately thereafter at the behest of Brébeuf. Aonetta had a strong influence over her nieces and nephews, encouraging them to grow up in the faith. Both Marie Aonetta and her husband, Joseph Chiwatenhwa, have been considered for sainthood in the Catholic Church.
• Echon, is the name given to Brébeuf by the Huron. It means "Healing Tree", as a representation of how much Brébeuf helped the Hurons and of the medicines he brought them from Europe. Another interpretation of Échon is "he who bears the heavy load", as Brébeuf was massive in stature and carried more than his share when working with the Huron people.
• Lake St. Isaac is named after Jouges, the namesake for the camp. This lake is used for organized swimming activities.
• Ahatsistari, honored as the greatest war chief of all the Huron nations, was accompanying Jogues, Goupil and Couture through enemy territory when the group was captured by the Mohawk Indians. Ahatsistari's name possibly means, "he who cooks with fire," which was fitting as he was a brutal warrior all the way to the end of his life, when he managed to literally spit fire at the Mohawk Indians who were torturing him.
• Couture, a French missionary who worked with Jogues among the Huron. He was ambushed and tortured by the Iroquois and witnessed Ahatsistari's death. Couture later became a part of the Iroquois councils when he impressed his captors with his endurance and continuous dignity throughout his torture. He was the only European to ever obtain such an honorable position, having risen from prisoner to chief.
• Teondechoren, brother of Joseph Chiwatenhwa, a Huron medicine man later turned missionary. Teondechoren refused baptism during Chiwatenhwa's lifetime but quickly converted days after his brother's surprise death and took on the name Joseph in honor of his brother. He carried on Chiwatenhwa's missionary work among the Huron. At one point he was a part of the missionary group that included Jogues, Couture, and Goupil who were captured and tortured by the Iroquois. The unit of Teondecoren used a slightly different spelling of his name.

Most campers stay in cabin groups called units. There is no electricity in most of the units. Each unit has potable water, an outhouse and campfire ring.

Units are one of four designs - tree house, cabin, cave or A-frame. Tree house units have 3 walls and an open entrance with catwalks connecting the cabins. The cave unit consists of platforms on the ground with no walls (two tree house style buildings are also in this unit). The A-frame unit has three buildings with screened in windows and doors. There are two different styles of cabin units.

Unit Name	Unit Type	Unit color	Mascot Animal	Cabin Name Inspiration	Notes
Amantacha	Tree House	Forest Green	Swallow	Grateful Dead
Brebeuf	Cabins	Royal Blue	Raccoon	Simon and Garfunkel	One of the original four units
Chabanel	Cave	Golden Yellow	Bear	Jethro Tull	One of the original four units
Daniel	Tree House	Black	Eagle	The Beatles
Garnier	Tree House	Kelly Green	Bobcat	Led Zeppelin
Goupil	Tree House	Purple	Fox	Bob Dylan	One of the original four units
Lalande	Tree House	Red	Owl	Tom Petty	One of the original four units
Lalemant	Tree House	Orange	Beaver	The Doors
Raganeau	Tree House	Turquoise	Squirrel	Pink Floyd	The oldest standing unit
Tekakwitha	A -Frame Lodges	Light Blue	Deer	Native American Tribes	Fully enclosed
Chiwatenwha	4 Sided Cabins	Light Green	Turtle	Fleetwood Mac	Fully enclosed
Aonetta	4 Sided Cabins	Pink	Hummingbird	Fleetwood Mac	Fully enclosed

Unit Name	Unit Type	Unit Color	Mascot Animal	Notes
Ahatsistari	Cabins	Light Brown	Rabbit	Originally a tent unit, cabins built later, then,after burning down, repurposed as an activity area
Couture	Tent	Light Blue	Butterfly	Various Locations; Lower Pakentuck, near main area, along Camp Road
Teondecoren	Tree house	Tan	Pheasant	Various iterations in the camp's history noted below

Teondecoren and Couture were originally designated as primitive units that gave campers an experience away from camp during which they lived off the land for the week. Teondecoren was later made into a tree house unit in 1973, then as a tepee unit in 1995. Couture was a tent unit as needed based on session enrollment.

BOQ - officially Bachelor Officers' Quarters but colloquially called "boys only quarters," though it can be used for campers and staff, male or female. This building is a fully enclosed cabin at group level and has electricity.

Lakeside - consists of a long bunkhouse style cabin as well as two smaller cabins.

Frontier Dorms - fully enclosed bunkhouses.

St. Noel - year-round lodging and retreat center.

The dining hall is a modern facility that can serve all of camp at one time. The building is heptagonal and has a fireplace in the center. It is located away from main camp, on top of the same hill as the stables. Most meals are served family style. The dining hall is air conditioned, and has windows on all sides to allow for ventilation. It is decorated with art work depicting camp that was created by current and former staff members as well as friends of camp. The dining hall had air conditioning installed for the summer of 2013.

The Health Center is equipped to handle guests throughout the year. It is staffed by medical professionals and on-call pediatric physicians every day of the summer. This facility has air conditioning.

The Old Dining Hall is still used for various programming including breakfast on the last day of each summer session and as a rainy day location.

The Trading Post sells food and items such as toiletries, camp gear, camp paraphernalia, ice cream and candy.

The St. Noel Lodge hosts the administrative offices of the camp and is also used for guest lodging year-round.

Pakentuck is a natural area that includes a waterfall and the remnant of a Boy Scout camp. Cedar Falls is the largest single, free-flowing waterfall in Illinois. The Pakentuck name comes from a Boy Scout group from Paducah, Kentucky.

Lake Echon drains via a small waterfall known as the Spillway. Formerly known as St. Catherine falls after St. Kateri Tekakwitha who took St. Catherine of Siena as her patron when she was baptized.

Split Rocks are common hike destinations. One of the split rocks is Augustine's Agony. Some others are Big Split, Little Split and Fat Man's Misery.

Hogg's Bluff is natural, stone peak jutting high above a lake. It was allegedly used as a trading post for Native Americans.

Bush's Garden is swimming hole downstream from the Spillway, popularized by a counselor with the last name Bushong, nickname Bush.

Cannonball Rock is a boulder in a stream that is popular for cannonball and other jumps into the water.

Pine Lake and Kane Lake are locations for swimming and camping.

Phantom's Canyon is near the west camping areas.

Program areas include an archery range, riflery range, handicrafts building, stables for horseback riding, a boating area for canoeing and kayaking, a swimming lake, a chapel, and other outdoor clearings for other programs such as woodsmanship. Many of the natural areas noted above are visited during daytime and overnight hikes.

Evenings include campfires, large group games, camping out overnight away from units, and an honor society ceremony. The first and last evenings of the summer program are held under a natural grotto. Mass is celebrated on Sunday evening during the summer program.

Most summer programs serve children and teenagers between the ages of 11 - 15. Campers arrive on Sunday and depart the following Saturday. Some programs have minimum age requirements. Activities are done in a centralized format where the entire unit typically participates together.

Designed with 8 to 10 year old campers in mind, mini camp is meant to be an introduction to the camp experience. The program is three days and three nights long while still including many of the activities of traditional camp. Some activities are modified to account for mini campers' age. The mini campers stay in enclosed cabin units, Aonnetta (girls) and Chiwatenwha (boys). Participants of the program stay in one of the units and are accompanied by extra staff members at all times. Mini camp explorers is for more adventurous 8 and 9-year-olds who feel capable of spending the entire week at camp. Because of the extended nature of their stay, campers are able to participate in all the activities of traditional camp in a modified form for their age and abilities. Campers spend their nights in either Chiwatenwha or Aonnetta with staff trained to take on the challenges of younger campers experiencing their first week-long sleepaway camp stay.

Camp Ondessonk offers specialized programs, referred to as adventure camp, that allow campers to focus on one set of skills in a particular area for an entire week. The main areas of focus are horsemanship, rock climbing, backpacking, mountain biking, and canoeing. The programs take a limited number of campers and provide them with the opportunity to enhance their knowledge and skills of a particular area. Campers are assisted by two or three specially trained staff members.

High school students learn to become counselors at the camp by participating in the Ondessonk Wisdom in Leadership (OWL) program and the Counselor In Training program (CIT). According to the camp's website, these programs are designed "for high school students who want to use their experience to grow socially and emotionally at Camp and beyond. Participants have the opportunity to learn about leadership styles, communication techniques and share and identify their own ideas and values. Participants will learn skills that last a lifetime."

The Loyal Lodge of Ondessonk & Tekakwitha is modeled after the honor camping society first established during Camp St. Philip in 1957. Induction into Lodge is open to campers, staff, and volunteers who demonstrate loyalty and dedication to camp in an exemplary way, and takes place each Thursday night during the summer in the Lodge ceremony. In order to be considered for Lodge, candidates much show these qualities as well as being at least a second year camper or staff member. Participants of both traditional camp and adventure programs are eligible. Members are divided geographically into councils for administrative purposes to give back to Ondessonk through fundraisers or service. Members of Lodge may also attend Fall and Spring Lodge Reunions each year. A member of Lodge is signified by a sash they wear, containing a patch of a simplified version of the symbol of Camp Ondessonk. General members wear red and blue sashes. Both are more simply referred to as Lodge members.

After being absent since the 1970s, the Lodge arrowhead was reestablished in 2007 and can be earned by Lodge members over time through dedication to Lodge. There are also two other honors awarded by the Lodge of Ondessonk and Tekakwitha. The St. John de Brebeuf Award is given to an active or associate member for rendering meritorious service to Camp Ondessonk, the Lodge service organization, and the community. The John de LaLande Award is presented to a non-Lodge Member who is part of the Camp Ondessonk staff and feels that they do not meet the proper requirements for membership into the organization but have rendered meritorious service to Camp Ondessonk and the community.

Lodge Camp allows campers to participate in traditional camp members with fellow Lodge members. Campers stay in a unit made up of other Lodge members and led by a Lodge Official on staff. As part of their experience Lodge Campers participate in rock climbing at Pakentuck, the High Challenge Course, and an extended horseback ride. They also perform a service project for Camp. Campers must be a member of the Loyal Lodge of Ondessonk and Tekakwitha in order to be eligible to attend. The program is open to campers meeting this requirement ages 11–16.

Beginning in the mid-1960s, Camp Ondessonk began organizing trips to destinations around the world as a reward for members of the Lodge of Ondessonk & Tekakwitha who sold specific quotas of advertisement space for the annual yearbook. Members were notified by a letter inviting them to participate free-of-charge. The trips took place over the Christmas holidays and went to places like Europe, Africa, and the Bahamas. They were usually 10 to 14 days long. In 1964 the trip left from Miami, Fl., on a yacht and sailed to the Bahama Islands for a Christmas vacation of swimming, beach combing, shopping, and relaxation. The 1971 trip took participants on an Iberian tour through Spain, Portugal, and Morocco. During one Lodge trips, which was in 1968 and went to Italy and Switzerland, the group attended Christmas Mass with the Pope and sat in ambassador seats just 20 feet from the Pope. They also spent New Year's Eve in Venice. The 1970 trip scheduled to tour the Middle East was canceled due to conflict in the region. The trips were eventually discontinued.

Camp Ondessonk is open year-round for camping, hiking, retreats, horseback trail rides and outdoor education programs for scouts and school groups. The camp also sponsors themed weekend events such as a father/son and mother/daughter camping events, a fall festival and work weekends to help improve the property. Third party organizations use the camp for events such the Southern Illinois Fat Tire Festival

The path of the April 8, 2024 total solar eclipse passed through the camp's property.

On July 7, 1981, a camper received a minor wound on his hand when he reached into Tommy the Bear's cage during feeding time and grabbed at Tommy's ears. The camper was treated by health services at camp, but the wound later became infected. A court ordered Tommy to be examined for rabies but this could only be accomplished by killing the bear so that his brain tissue could be examined. This court order was appealed and after multiple legal proceedings, the injured camper's family dropped the lawsuit.

An Albuquerque man filed a lawsuit alleging that he was sexually abused by a former director while he was a camper in 1981. The camp and the Diocese of Belleville were eventually dismissed in the district court.

A lawsuit was filed for negligence against the camp for not properly safeguarding a cliff after an accident on 10 April 1992. A district court granted summary judgment to the Catholic Diocese of Belleville. The case was appealed and the decision in favor of the Catholic Diocese of Belleville was affirmed.