Onondaga County (/ˌɒnənˈdɑːɡə/ ON-ən-DAH-gə) is a county in the U.S. state of New York. As of the 2020 census, the population was 476,516. The county seat is Syracuse. The county is part of the Central New York region of the state.

Onondaga County is the core of the Syracuse Metropolitan Statistical Area.

The name Onondaga derives from the name of the Native American tribe indigenous to this area, one of the original Five Nations of the Haudenosaunee. They call themselves (autonym) Onoda'gega, sometimes spelled Onontakeka. The word means "People of the Hills." Sometimes the term is Onondagaono ("The People of the Hills"). The federally recognized Onondaga Nation has a 9.3 square miles (24 km) reservation within the county, on which they have self-government.

When counties were established in New York in 1683, the present Onondaga County was part of Albany County. This enormous county included the northern part of New York State as well as all of the present State of Vermont and, in theory, extended westward to the Pacific Ocean. It was reduced in size on July 3, 1766, by the creation of Cumberland County, and further on March 16, 1770, by the creation of Gloucester County, both containing territory now in Vermont.

On March 12, 1772, what was left of Albany County was split into three parts, one remaining under the name Albany County. One of the other pieces, Tryon County, contained the western portion (and thus, since no western boundary was specified, theoretically still extended west to the Pacific). The eastern boundary of Tryon County was approximately 5 miles (8 km) west of the present city of Schenectady, and the county included the western part of the Adirondack Mountains and the area west of the West Branch of the Delaware River. The area then designated as Tryon County now includes 37 counties of New York State. The county was named for William Tryon, colonial governor of New York.

In the years prior to 1776, most of the Loyalists in Tryon County fled to Canada. The Onondaga were among four Iroquois tribes that allied with the British against the American colonists, as they hoped to end their encroachment. Instead, they were forced to cede most of their land in New York to the United States after the war. Many Onondaga went with Joseph Brant and other nations to Canada, where they received land grants in compensation and formed the Six Nations of the Grand River First Nation.

In 1784, after a peace treaty ended the American Revolutionary War, the name of Tryon County was changed to Montgomery County. It honored General Richard Montgomery, who had captured several places in Canada and died attempting to capture the city of Quebec, and replaced the name of the hated British governor.

In 1789, Montgomery County was reduced by the splitting off of Ontario County from Montgomery. The actual area split off from Montgomery County was much larger than the present county, also including the present Allegany, Cattaraugus, Chautauqua, Erie, Genesee, Livingston, Monroe, Niagara, Orleans, Steuben, Wyoming, Yates, and part of Schuyler and Wayne Counties.

In 1791, Herkimer County was one of three counties split off from Montgomery (the other two being Otsego, and Tioga County). This was much larger than the present county, however, and was reduced by a number of subsequent splits.

In 1794, Onondaga County was split off from Herkimer County. This county was larger than the current Onondaga County, including the present Cayuga, Cortland, and part of Oswego Counties.

In 1799, Cayuga County was split off from Onondaga.

In 1808, Cortland County was split off from Onondaga.

In 1816, parts of Oneida and Onondaga Counties were taken to form the new Oswego County.

At the time Onondaga County was organized, it was divided into eleven towns: Homer, Pompey, Manlius, Lysander, Marcellus, Ulysses, Milton, Scipio, Ovid, Aurelius and Romulus.

Central New York developed rapidly after the New Military Tract provided land in lieu of payment to Revolutionary War veterans. Migration was largely from the east, mostly from New England states. The Genesee Road, which became the Seneca Turnpike in 1800, provided access. Generally settlers preferred higher land, since they associated lowlands with disease. Over time, as early clearing and farming eroded hillside soil, valley lands were more fertile and highly prized for agriculture as well as for water power, which was the origin of many communities. An early settler of 1823 was James Hutchinson Woodworth, a native of Washington County, NY. He helped clear land for his family's farm in this region before he moved to Chicago where he became Mayor. The completion of the Erie Canal across New York state in 1825 accelerated trade, development and migration.

The city of Syracuse, New York developed relatively late, due to its marshy situation. It was incorporated as a village in 1825 and as a city in 1847; by contrast, the Village of Manlius, along the Cherry Valley and Seneca Turnpikes, was incorporated in 1813. The population of these rural towns was greatest in the late nineteenth century, when more people cultivated land and farms were relatively small, supporting large households.

Since that time, agriculture has declined in the county. Some Onondaga County towns like Spafford were largely depopulated and many villages became veritable ghost towns. Onondaga County highlands now are more heavily reforested, with public parks and preserves providing recreation. Two Finger Lakes in the county, Skaneateles and Otisco, also attract visitors. The village of Skaneateles on scenic Route 20 has become a major tourist destination.

At the turn of the twenty-first century, population declined in the City of Syracuse while suburban communities generally grew, particularly with tract developments north of the city. Elsewhere, scattered commuter houses appeared, generally on fairly large parcels. The rapid development of the village of Skaneateles and shores of Skaneateles Lake led to increased demand for property and property values.

According to the U.S. Census Bureau, the county has an area of 806 square miles (2,090 km), of which 778 square miles (2,020 km) is land and 27 square miles (70 km) (3.4%) is water. The geographic dimensions of the county are illustrated as approximately 35 miles (56 km) in length and 30 miles (48 km) in width, and comprising 25 miles (40 km) of the New York State Barge Canal System, in combination with a number of lakes, streams and rivers. Onondaga County is in the central portion of New York State, west of Albany and Utica, east of Rochester and northeast of Ithaca. Onondaga Lake is bordered by many of the larger communities in the county. The highest point in Onondaga County is at 2057 feet, along Morgan Hill located just east of Morgan Hill State Forest on private property. The second highest point in Onondaga County is at 2019 feet elevation and on the summit of Fellows Hill which is located in Morgan Hill State Forest near Fabius and Apulia south of state route 80.

The northern part of the county is fairly level lake plain, extending northward to Lake Ontario. Oneida Lake three rivers, as well as the Erie and subsequent Barge Canals are in the lake plain. The main line of the New York Central Railroad and the New York State Thruway extend east and west across the county through the lake plain. The southern part of the county is Appalachian Plateau, with high hills rising at the southern edge of Syracuse. This is the eastern part of the Finger Lakes region. Skaneateles Lake and Otisco Lake are both in Onondaga County. US 20 extends east and west across the county, traversing dramatic hill-and-valley terrain. Between the lake plain and Appalachian highlands is a zone noted for drumlins, smaller, scattered hills formed as mounds of debris left by the last glacier. Tully is geologically noted for the terminal moraine deposited there by the glacier, filling the deep Tully Valley, which might have been another Finger Lake had the moraine been left closer to Syracuse, impounding water. Tully is at the divide between two major watersheds, one flowing northward to the Atlantic Ocean by way of the St. Lawrence River and the other southward to the ocean via the Susquehanna River. Oneida Lake, the Finger Lakes, and smaller bodies of water provide recreation. The Appalachian hills have several ski areas, waterfalls and historic villages as well as large parks and forest preserves.

• Jamesville Reservoir
• Oneida Lake
• Onondaga Lake
• Otisco Lake
• Skaneateles Lake

• Oswego County – north
• Madison County – east
• Cortland County – south
• Cayuga County – west

Historical population

Census	Pop.	Note	%±
1800	7,406		—
1810	25,987		250.9%
1820	41,467		59.6%
1830	58,973		42.2%
1840	67,911		15.2%
1850	85,890		26.5%
1860	90,686		5.6%
1870	104,183		14.9%
1880	117,893		13.2%
1890	146,247		24.1%
1900	168,735		15.4%
1910	200,298		18.7%
1920	241,465		20.6%
1930	291,606		20.8%
1940	295,108		1.2%
1950	341,719		15.8%
1960	423,028		23.8%
1970	472,746		11.8%
1980	463,920		−1.9%
1990	468,973		1.1%
2000	458,336		−2.3%
2010	467,026		1.9%
2020	476,516		2.0%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010-2019

As of the census of 2000, the county had 458,336 people, 181,153 households, and 115,394 families. The population density was 587 inhabitants per square mile (227/km). There were 196,633 housing units at an average density of 252 units per square mile (97/km). The county's racial makeup was 84.78% White, 9.38% African American, 0.86% Native American, 2.09% Asian, 0.03% Pacific Islander, 0.89% from other races, and 1.97% from two or more races. Hispanics or Latinos of any race were 2.44% of the population. About 17.5% were of Italian, 16.2% Irish, 12.4% German, 9.4% English, and 6.0% Polish ancestry according to the 2000 United States Census, and 91.4% spoke English, 2.4% Spanish and 1.1% Italian as their first language.

Of the 181,153 households, 31.90% had children under age 18 living with them, 46.90% were married couples living together, 12.90% had a female householder with no husband present, and 36.30% were not families. About 29.40% of all households were made up of individuals, and 10.80% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 3.07.

25.80% of the county's population was under age 18, 9.50% was from age 18 to 24, 28.80% was from age 25 to 44, 22.10% was from age 45 to 64, and 13.80% was age 65 or older. The median age was 36 years. For every 100 females, there were 91.70 males. For every 100 females age 18 and over, there were 87.70 males.

The county's median household income was $40,847, and the median family income was $51,876. Males had a median income of $39,048 versus $27,154 for females. The county's per capita income was $21,336. About 8.60% of families and 12.20% of the population were below the poverty line, including 15.50% of those under age 18 and 7.10% of those age 65 or over.

Onondaga County Racial Composition

Race	Num.	Perc.
White (NH)	347,290	73%
Black or African American (NH)	54,410	11.42%
Native American (NH)	2,940	0.62%
Asian (NH)	20,119	4.22%
Pacific Islander (NH)	106	0.02%
Other/Mixed (NH)	25,079	5.26%
Hispanic or Latino	26,572	5.57%

Onondaga County is home to Syracuse University, a major research university and SUNY Upstate Medical University, a public medical school. Upstate Medical University is the largest producer of jobs in the region with a direct workforce of 10,959 employees.

Other higher educational institutions include SUNY Oswego’s Syracuse Campus, Le Moyne College, SUNY College of Environmental Science and Forestry, Onondaga Community College, St. Joseph's College of Nursing, and several for-profit colleges.

K-12 school districts which cover parts of the county include:

United States presidential election results for Onondaga County, New York

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	93,916	40.84%	133,155	57.91%	2,871	1.25%
2020	91,715	38.85%	138,991	58.88%	5,362	2.27%
2016	83,649	40.13%	112,337	53.89%	12,454	5.97%
2012	78,831	38.51%	122,254	59.72%	3,632	1.77%
2008	84,972	38.94%	129,317	59.25%	3,950	1.81%
2004	94,006	43.80%	116,381	54.23%	4,238	1.97%
2000	83,678	41.09%	109,896	53.97%	10,069	4.94%
1996	73,771	37.84%	100,190	51.40%	20,978	10.76%
1992	77,642	36.13%	90,645	42.18%	46,620	21.69%
1988	104,080	51.91%	94,751	47.26%	1,654	0.82%
1984	121,857	59.64%	81,777	40.03%	680	0.33%
1980	97,887	50.65%	73,453	38.00%	21,940	11.35%
1976	115,474	59.96%	76,097	39.51%	1,007	0.52%
1972	140,039	69.18%	61,895	30.58%	482	0.24%
1968	95,806	50.46%	83,576	44.02%	10,483	5.52%
1964	63,205	32.92%	128,630	66.99%	179	0.09%
1960	107,170	54.08%	90,836	45.84%	150	0.08%
1956	137,852	73.42%	49,918	26.58%	0	0.00%
1952	119,268	64.96%	64,022	34.87%	302	0.16%
1948	84,370	53.86%	66,295	42.32%	5,983	3.82%
1944	80,507	52.06%	73,562	47.57%	569	0.37%
1940	91,056	57.26%	67,481	42.44%	485	0.30%
1936	80,498	55.03%	62,945	43.03%	2,827	1.93%
1932	66,363	49.81%	62,227	46.71%	4,629	3.47%
1928	76,278	57.04%	54,706	40.91%	2,732	2.04%
1924	65,395	64.90%	24,773	24.58%	10,601	10.52%
1920	57,008	66.25%	23,308	27.09%	5,731	6.66%
1916	27,815	55.35%	19,892	39.58%	2,546	5.07%
1912	16,202	35.29%	15,827	34.47%	13,888	30.25%
1908	27,209	58.70%	16,643	35.90%	2,503	5.40%
1904	27,115	62.60%	14,633	33.78%	1,569	3.62%
1900	24,317	59.37%	14,698	35.89%	1,942	4.74%
1896	25,032	62.36%	13,695	34.12%	1,414	3.52%
1892	19,008	52.94%	14,900	41.50%	1,996	5.56%
1888	20,144	57.65%	14,001	40.07%	796	2.28%
1884	16,892	54.92%	13,166	42.81%	700	2.28%

Onondaga County was governed exclusively by a board of supervisors until 1961, when voters approved the creation of the county executive. In 1968, the board reorganized into a 24-seat county legislature. In 2001, the legislature was reduced to 19 seats. In 2010, voters approved a measure to reduce the legislature to 17 seats. None of the legislative seats, nor the county executive's seat, are at-large. Currently, there are 11 Republicans and 6 Democrats. J. Ryan McMahon II (R) is the current County Executive.

Historically, Onondaga County was a Republican stronghold, like most of Central New York. From 1856 to 1988, the GOP carried the county in all but one presidential election, Lyndon B. Johnson's landslide in 1964. Since 1992, the county has gone Democratic in every presidential election, much like many urban counties around the country. However, it is a swing county in congressional, state and local races. Onondaga is entirely located within New York's 22nd Congressional District, represented by Republican Brandon Williams. Democratic strength is concentrated in Syracuse itself, while Republicans do well in the suburbs.

Onondaga County Executives

Name	Party	Term
John H. Mulroy	Republican	January 1, 1962 – December 31, 1987
Nicholas J. Pirro	Republican	January 1, 1988 – December 31, 2007
Joanne M. Mahoney	Republican	January 1, 2008 – November 1, 2018
J. Ryan McMahon, II	Republican	November 1, 2018 –

Onondaga County Legislature

District	Legislator	Party	Residence
1	Brian F. May, Majority Leader	Republican	Baldwinsville
2	Kevin J. Meaker	Republican	Clay
3	Timothy T. Burtis, Chairman	Republican	Cicero
4	Colleen A. Gunnip	Republican	Liverpool
5	Debra J. Cody	Republican	North Syracuse
6	Julie Abbott	Republican	Skaneateles
7	Dan Romeo	Democratic	Syracuse
8	Christopher J. Ryan, Minority Leader	Democratic	Syracuse
9	Palmer Harvey	Democratic	Syracuse
10	Mark A. Olson	Republican	Fayetteville
11	Richard McCarron	Republican	Syracuse
12	David H. Knapp	Republican	LaFayette
13	Ken Bush Jr.	Republican	Jordan
14	Cody M. Kelly	Republican	Clay
15	Maurice Brown	Democratic	Syracuse
16	Charles E. Garland	Democratic	Syracuse
17	Nodesia R. Hernandez	Democratic	Syracuse

As of 2021, the sheriff of Onondaga County is Eugene J. Conway. Along with Broome County, New York, Onondaga County was sued in 2017 over placing juvenile inmates in solitary confinement.

Syracuse, the county seat, is the only city in Onondaga County. The following is a list of official towns, villages, and hamlets.

#	Location	Population	Type	Area
1	†Syracuse	148,620	City	Greater Syracuse
2	Lysander	23,074	CDP	West
3	De Witt	11,247	CDP	Greater Syracuse
4	Fairmount	10,248	CDP	Greater Syracuse
5	Baldwinsville	7,898	Village	West
6	Radisson	7,038	CDP	North
7	North Syracuse	6,739	Village	North
8	Solvay	6,645	Village	Greater Syracuse
9	Mattydale	6,296	CDP	Greater Syracuse
10	Westvale	5,090	CDP	Greater Syracuse
11	Manlius	4,662	Village	East
12	Galeville	4,482	CDP	Greater Syracuse
13	Lyncourt	4,376	CDP	Greater Syracuse
14	Fayetteville	4,225	Village	East
15	‡Brewerton	3,907	CDP	North
16	Village Green	3,834	CDP	West
17	Minoa	3,657	Village	East
18	East Syracuse	3,078	Village	Greater Syracuse
19	Lakeland	2,556	CDP	Greater Syracuse
20	Skaneateles	2,533	Village	West
21	Liverpool	2,242	Village	Greater Syracuse
22	Nedrow	2,095	CDP	Greater Syracuse
23	Seneca Knolls	1,992	CDP	West
24	Marcellus	1,745	Village	West
25	‡Bridgeport	1,389	CDP	East
26	Camillus	1,222	Village	Greater Syracuse
27	Jordan	1,192	Village	West
28	Elbridge	921	Village	West
29	Tully	904	Village	South
30	Fabius	309	Village	South

† - County seat

‡ - Not entirely in Onondaga County

• Onondaga Reservation

• List of bus routes in Onondaga County, New York
• List of counties in New York
• National Register of Historic Places listings in Onondaga County, New York
• Onondaga Creek
• Timeline of town creation in Onondaga County

• Sullivan, James; Williams, Melvin E.; Conklin, Edwin P.; Fitzpatrick, Benedict, eds. (1927), "Chapter XI. Onondaga County.", History of New York State, 1523–1927 (PDF), vol. 2, New York City, Chicago: Lewis Historical Publishing Co., p. 773-81, hdl:2027/mdp.39015019994048, Wikidata Q114149636

• Onondaga County, NY official site
• Onondaga County, NY US GenWeb Project
• Onondaga County, NY U.S. Census Page
• Onondaga County Historical Aerial Photographs of New York , Cornell University Library & Cornell Institute for Resource Information Sciences

43°01′N 76°12′W / 43.01°N 76.20°W / 43.01; -76.20