Shiawassee County (/ˌʃaɪəˈwɒsi/ SHY-ə-WOSS-ee) is a county located in the U.S. state of Michigan. As of the 2020 United States Census, the population was 68,094. The county seat is Corunna, and the largest city in the county is Owosso. In 2010, the center of population of Michigan was located in Shiawassee County, in Bennington Township.

Shiawassee County is included in the Lansing-East Lansing, MI Metropolitan Statistical Area.

In 1822, the Michigan Territorial legislature defined a new county, Shiawassee (named for the river), taken from portions of existing Oakland and St. Clair counties. However, for purposes of representation, revenue, and judicial matters, the area was temporarily assigned to adjoining county governments. In early 1837, the Michigan Territory was admitted into the Union as the State of Michigan, and that same year the new Michigan State government authorized the organization of a county government in Shiawassee.

According to the US Census Bureau, the county has a total area of 541 square miles (1,400 km), of which 531 square miles (1,380 km) is land and 10 square miles (26 km) (1.9%) is water. The Shiawassee River enters it from Genesee County in the southeast and flows through Corunna and Owosso in the center of the county, exiting to Saginaw County in the north. Shiawassee County is considered to be a part of Central Michigan.

• I-69 - enters near SW corner of county. Runs ENE past Shaftsburg, Perry, Morrice, Bancroft, Durand. Exits running east into Genesee County.
• M-13 - runs along the east line of county, from NE corner to intersection with I-69 one mile (1.6 km) south of Lennon.
• M-21 - runs east–west through upper middle of county, passing Corunna and Owosso.
• M-52 - enters north line of county at Oakley. Runs south to Owosso, then SW and south to Perry. Exits running south into Ingham County.
• M-71 - begins at Owosso. Runs ESE to intersection with I-69, one mile (1.6 km) NW of Durand.

• Durand Union Station in Durand offers access to Amtrak's Blue Water route. The train runs from Port Huron to Chicago.

Owosso Community Airport – 2 miles (3.2 km) east of Owosso. Public airport for general aviation, primarily smaller aircraft.

Historical population

Census	Pop.	Note	%±
1840	2,103		—
1850	5,230		148.7%
1860	12,349		136.1%
1870	20,858		68.9%
1880	27,059		29.7%
1890	30,952		14.4%
1900	33,866		9.4%
1910	33,246		−1.8%
1920	35,924		8.1%
1930	39,517		10.0%
1940	41,207		4.3%
1950	45,967		11.6%
1960	53,446		16.3%
1970	63,075		18.0%
1980	71,140		12.8%
1990	69,770		−1.9%
2000	71,687		2.7%
2010	70,648		−1.4%
2020	68,094		−3.6%
2023 (est.)	68,025		−0.1%
US Decennial Census 1790-1960 1900-1990 1990-2000 2010-2018

As of the 2010 United States Census, Shiawassee County had a 2010 population of 70,648. This decrease of -1,039 people from the 2000 United States Census represents a decrease of 1.4% during that ten-year period. In 2010 there were 27,481 households and 19,397 families in the county. The population density was 133.1 per square mile (51.4 per square kilometer). There were 30,319 housing units at an average density of 57.1 per square mile (22.0/km). 96.7% of the population were White, 0.5% Native American, 0.5% Black or African American, 0.4% Asian, 0.5% of some other race and 1.5% of two or more races. 2.4% were Hispanic or Latino (of any race). 22.2% were of German, 21.8% English, 9.5% Irish, 5.2% French, French Canadian or Cajun and 5.1% Polish ancestry according to 2010 American Community Survey. As of the 2020 Census, Shiawassee County had a population of 68,094 people.

There were 27,481 households, out of which 32.5% had children under the age of 18 living with them, 53.8% were husband and wife families, 11.6% had a female householder with no husband present, 29.4% were non-families, and 24.2% were made up of individuals. The average household size was 2.54 and the average family size was 2.99.

The county population contained 24.1% under age of 18, 8.5% from 18 to 24, 23.9% from 25 to 44, 29.1% from 45 to 64, and 14.3% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 97.7 males. For every 100 females age 18 and over, there were 94.6 males.

The 2010 American Community Survey 1-year estimate indicates the median income for a household in the county was $46,528 and the median income for a family was $52,614. Males had a median income of $32,155 versus $19,301 for females. The per capita income for the county was $21,103. About 10.6% of families and 15.4% of the population were below the poverty line, including 22.1% of those under the age 18 and 5.8% of those age 65 or over.

Shiawassee County has tended to vote Republican since the beginning. Since 1884, the Republican Party nominee for president has carried 75% of the elections (27 of 36). Until the 2020 U.S. presidential election, the county was a U.S. presidential bellwether county, voting for the winner of the U.S. presidential election from 1980 to 2016.

United States presidential election results for Shiawassee County, Michigan

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	24,718	60.65%	15,335	37.63%	699	1.72%
2020	23,149	58.90%	15,347	39.05%	805	2.05%
2016	19,230	56.37%	12,546	36.78%	2,335	6.85%
2012	15,962	47.39%	17,197	51.06%	520	1.54%
2008	16,268	44.67%	19,397	53.27%	750	2.06%
2004	19,407	52.95%	16,881	46.06%	363	0.99%
2000	15,816	49.09%	15,520	48.17%	882	2.74%
1996	11,714	38.56%	14,662	48.27%	3,999	13.17%
1992	10,930	33.78%	12,629	39.03%	8,801	27.20%
1988	15,506	53.94%	13,056	45.42%	186	0.65%
1984	18,756	65.97%	9,514	33.46%	161	0.57%
1980	15,756	51.71%	11,985	39.33%	2,729	8.96%
1976	15,113	54.52%	12,202	44.02%	406	1.46%
1972	15,489	61.62%	8,932	35.53%	715	2.84%
1968	11,465	50.88%	8,619	38.25%	2,448	10.86%
1964	7,786	36.21%	13,676	63.60%	41	0.19%
1960	13,757	60.86%	8,773	38.81%	74	0.33%
1956	14,600	67.75%	6,873	31.89%	78	0.36%
1952	13,562	68.41%	6,056	30.55%	206	1.04%
1948	10,377	66.97%	4,852	31.31%	267	1.72%
1944	11,601	68.41%	5,292	31.21%	64	0.38%
1940	9,995	63.24%	5,727	36.24%	82	0.52%
1936	6,017	43.36%	6,666	48.03%	1,195	8.61%
1932	6,600	44.19%	8,002	53.58%	334	2.24%
1928	9,851	79.40%	2,496	20.12%	60	0.48%
1924	8,987	72.99%	1,738	14.12%	1,588	12.90%
1920	7,194	69.93%	2,595	25.23%	498	4.84%
1916	3,926	51.29%	3,308	43.22%	420	5.49%
1912	2,309	30.05%	1,957	25.47%	3,417	44.47%
1908	4,199	57.96%	2,339	32.28%	707	9.76%
1904	5,553	66.19%	2,241	26.71%	596	7.10%
1900	5,051	56.69%	3,441	38.62%	418	4.69%
1896	4,654	50.50%	4,303	46.69%	259	2.81%
1892	3,619	47.17%	2,994	39.02%	1,060	13.81%
1888	4,007	51.91%	3,187	41.29%	525	6.80%
1884	2,705	41.71%	3,141	48.43%	640	9.87%

The county government operates the jail, maintains rural roads, operates the major local courts, records deeds, mortgages, and vital records, administers public health regulations, and participates with the state in the provision of social services. The county board of commissioners controls the budget and has limited authority to make laws or ordinances. In Michigan, most local government functions — police and fire, building and zoning, tax assessment, street maintenance, etc. — are the responsibility of individual cities and townships.

On July 25, 2021, it was revealed that the county's board of commissioners paid themselves a total of $65,000 out of a $557,000 federal relief funds earmarked for county employee hazard pay due to the COVID-19 pandemic. Employees typically received $1,000 to $2,000. The seven member board of commissioners voted themselves $5,000 for four members, $10,000 for two, and the chairman of the county commissioners $25,000. Following days of criticism, a Shiawassee prosecutor declared the bonuses illegal; commissioners responded that they would return the money.

(information as of January 2023)

• Caledonia Charter Township
• Owosso Charter Township

• Henderson
• Middletown

• List of Michigan State Historic Sites in Shiawassee County, Michigan
• National Register of Historic Places listings in Shiawassee County, Michigan

• Shiawassee County History
• Shiawassee County website
• City of Corunna, Michigan
• "Bibliography on Shiawassee County". Clarke Historical Library, Central Michigan University.
• Owosso Independent

42°57′N 84°08′W / 42.95°N 84.14°W / 42.95; -84.14