Onalaska is an unincorporated community and census-designated place (CDP) in Lewis County, Washington, United States. As of the 2020 census it had a population of 657. Onalaska is located along Washington State Route 508.

The name for the community comes from the poem "The Pleasures of Hope" by Scottish poet Thomas Campbell. The place referenced in the poem was called Oonalaska, which was shortened. This name was given to a lumber town in Arkansas. After that was a success, the next operation, in Wisconsin, was also named Onalaska. The name became a company tradition, with the towns of Onalaska, Wisconsin and Onalaska, Texas still surviving.

Onalaska was built around the inland mill established by the Carlisle Lumber Company in 1909, with actual production commencing in 1914. At its peak in 1929, company inventory numbered over 20 million board feet of lumber — enough to stretch all the way to the Panama Canal. The company closed down the mill and the Carlisle family left the town following issues with unionization in the late 1940s, which they decided not to combat.

The company's surviving 225-foot smokestack near Carlisle Lake was built around 1920, and is the last trace of one of the most successful mid-sized sawmills in Washington state. In May 2021, the site was listed to the Washington Heritage Register by the Washington State Advisory Council on Historic Preservation.

The mill employed a significant number of Japanese and Japanese Americans. They lived north of today's State Route 508 and east of Carlisle Avenue. The streets, which ran parallel to Carlisle Avenue were called Oriental Avenue, Nippon Avenue and Tokyo Avenue.

According to Onalaska, a history of the Carlisle Lumber Company by Vic Kucera, the 1940 census showed 62 people of Japanese descent living in Lewis County. Because of their experience in the mill, the local Japanese Americans were forced to relocate to Camp Tulelake in California to help with its construction, Kucera writes. The Army relied on their labor to finish the camp where they were subsequently interned for the duration of WWII.

The Lewis County Museum in Chehalis has an exhibit honoring the Japanese and Japanese American internees.

In 2014, Governor Jay Inslee awarded $20,000 to Onalaska Wood Energy during his Climate Tour that year, and praised the company as “one of the leaders in biofuel technology.” By 2020, the company had left 100,000 gallons of hazardous waste and in 2021 the EPA started an emergency $0.9 million cleanup, shipping the waste by truck and railroad to Idaho and Utah.

Onalaska is in west-central Lewis County, in the valley of the South Fork of the Newaukum River. State Route 508 passes through the community, leading west 9 miles (14 km) to Napavine and east 24 miles (39 km) to Morton. Chehalis, the Lewis county seat, is 14 miles (23 km) northwest of Onalaska.

According to the U.S. Census Bureau, the Onalaska CDP has an area of 1.6 square miles (4.2 km), all of it recorded as land. The South Fork of the Newaukum forms the southern edge of the community, and Carlisle Lake is on the western edge. The Newaukum River flows west to the Chehalis River at Chehalis.

Held for the first time in 2009, the Onalaska Apple Harvest Festival is an annual community celebration usually held in late September or early October. Notable highlights of the event include an apple pie contest, a parade, farm tours, a community-wide church service, various cuisine options, high school alumni sporting competitions, canoe and kayak races, and a "royal court" bingo tournament. Profits and donations from the festival help fund community projects in Onalaska. Organized by the Onalaska Alliance, the group also oversees a yearly Easter egg hunt in the town.

The community is home to Carlisle Lake Park. Acquired in 2012 by the non-profit group, Onalaska Alliance, the park has added paved trails, parking, and bathroom facilities. As of 2024, the park is under the ownership of the alliance and free to use. The lake is privately owned but visitors can access the waters and fish at the lake.

Onalaska is an unincorporated community and has no mayor, city council, or other town government. The Onalaska Alliance is usually recognized as a major community leader, running the Apple Harvest Festival, maintaining Carlisle Lake, and cooperating with the school district and local businesses to better the town.

Presidential Elections Results

Year	Republican	Democratic	Third parties
2020	70.35% 968	26.74% 368	2.25% 31

Onalaska is recognized as being majority Republican and conservative, similar in respects to other rural populations within Lewis County.

Third parties receiving votes in the 2020 election were for candidates of the Libertarian Party and Green Party, and there were 8 votes for write-in candidates.

The Onalaska School District provides the community's education, including preschool programs

• Onalaska Elementary/Middle School (OEMS)
• Onalaska High School

The high school provides several "workplace-style" classes, including an aquaculture program in which students, in conjunction with local Native American communities and the school, operate a fish hatchery, the only school in the state to do so as of 2017. The curriculum began as a partnership with a coal plant in the early 1990s, as a mitigation strategy on the Skookumchuck River. In 2023, the students released a combined 135,000 coho and steelhead hatchlings above a dam on Carlisle Lake into Gheer Creek. Students can also take a natural resource class, which provides training in brush and field work. There are courses for wood and metal working and a school club that teaches outdoor skills.

Onalaska is home to the Ed Herold Observatory, named after an amateur astronomer who raised the funds for the construction. Built by community volunteer efforts, the telescope is the second largest public telescope in the state, measuring a half-inch less than the astronomical equipment at the Goldendale Observatory. An after-school astronomy program utilizes the telescope, which itself was named after a volunteer.

The entire Onalaska High School graduating class of 2017, a total of 43 students, were accepted into a college. The 100% rate was part of a statewide initiative, the High School and Beyond Plan, that the school district implemented via a required class called "Senior Success".

The Onalaska School District has teams in football, basketball, track, and volleyball, among other sports. Teams representing Onalaska are usually called the Loggers. The high school football team won the Class 2B State Championship in 2019.

Onalaska is near two privately-owned airfields. Four miles east of Onalaska, in an area that was once the small community of Burnt Ridge, is a 2,000 foot (610 metres) runway known as the Burnt Ridge Airstrip (WN74). Directly south of the community is Nelsons Nitch Airport (WN59) that contains a 1,850 feet (563.9 m) landing strip.

• Onalaska Alliance
• Onalaska School District