Isabella County is a county located in the U.S. state of Michigan. As of the 2020 Census, the population was 64,394. Its county seat is Mount Pleasant. The area was known as Ojibiway Besse, meaning "the place of the Ojibwa". Isabella County contains the Isabella Indian Reservation, on which members of the Saginaw Chippewa Tribal Nation live.

Isabella County was described by action of the Michigan Territory legislature in 1831, but for purposes of population, revenue, and judicial matters, it was assigned to nearby counties. Its area was partitioned from unorganized territory plus a portion of Mackinac, which had existed as a Territorial County since 1818.

The Michigan Territory was admitted to the Union as Michigan state in early 1837. By 1859, Isabella had sufficient settlement and interest in self-government that the state legislature authorized its organization. Based on a suggestion by Henry Rowe Schoolcraft, the U.S. Indian agent in this area, the county was named after Queen Isabella I of Castile, who with her husband Ferdinand commissioned Columbus's expedition to the New World.

Isabella County comprises the Mount Pleasant, Michigan micropolitan statistical area in Mid-Michigan. The county contains the Isabella Indian Reservation, which has a total area of 217.67 square miles (563.8 km). It is the major land base of the federally recognized Saginaw Chippewa Tribal Nation. Part of the county seat of Mount Pleasant is located within the reservation.

According to the US Census Bureau, the county has a total area of 578 square miles (1,500 km), of which 573 square miles (1,480 km) are land and 5.0 square miles (13 km) (0.9%) are water.

• US 10 – cuts across NE corner of county. Enters at Clare; runs ESE to east county line. Exits to Coleman.
• US 127 – runs north–south through the eastern central part of county. Passes Rosebush and Mt. Pleasant, runs SE to Shepherd, then runs south into Gratiot County.
• M-20 – runs east–west across lower central part of county. Enters from Remus. Ends at Mt. Pleasant.
• (proposed) – I-73 - project in Michigan is inactive

Historical population

Census	Pop.	Note	%±
1860	1,443		—
1870	4,113		185.0%
1880	12,159		195.6%
1890	18,784		54.5%
1900	22,784		21.3%
1910	23,029		1.1%
1920	22,610		−1.8%
1930	21,126		−6.6%
1940	25,982		23.0%
1950	28,964		11.5%
1960	35,348		22.0%
1970	44,594		26.2%
1980	54,110		21.3%
1990	54,624		0.9%
2000	63,351		16.0%
2010	70,311		11.0%
2020	64,394		−8.4%
2023 (est.)	64,118		−0.4%
US Decennial Census 1790-1960 1900-1990 1990-2000 2010-2018

As of the 2000 United States Census, there were 63,351 people, 22,425 households, and 13,006 families residing in the county. The population density was 110 people per square mile (42 people/km). There were 24,528 housing units at an average density of 43 per square mile (17/km). The racial makeup of the county was 91.51% White, 2.75% Native American, 1.93% Black or African American, 1.40% Asian, 0.05% Pacific Islander, 0.68% from other races, and 1.68% from two or more races. 2.24% of the population were Hispanic or Latino of any race. 28.0% were of German, 10.1% English, 10.0% Irish, 7.5% American and 6.0% Polish ancestry, 95.9% spoke English and 1.6% Spanish as their first language.

There were 22,425 households, out of which 28.40% had children under the age of 18 living with them, 45.40% were married couples living together, 8.90% had a female householder with no husband present, and 42.00% were non-families. 23.80% of all households were made up of individuals, and 7.30% had someone living alone who was 65 years of age or older. The average household size was 2.55 and the average family size was 3.03.

The county population contained 20.30% under the age of 18, 29.40% from 18 to 24, 23.80% from 25 to 44, 17.40% from 45 to 64, and 9.00% who were 65 years of age or older. The median age was 25 years. For every 100 females there were 91.40 males. For every 100 females age 18 and over, there were 88.60 males.

The median income for a household in the county was $34,262, and the median income for a family was $45,953. Males had a median income of $32,270 versus $24,180 for females. The per capita income for the county was $16,242. 7.40% of families and 20.40% of the population were below the poverty line, including 11.30% of those under age 18 and 7.80% of those age 65 or over.

United States presidential election results for Isabella County, Michigan

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	16,320	52.82%	14,011	45.34%	569	1.84%
2020	14,815	50.26%	14,072	47.74%	589	2.00%
2016	12,338	48.31%	11,404	44.65%	1,798	7.04%
2012	10,800	44.52%	13,038	53.74%	422	1.74%
2008	11,220	39.49%	16,679	58.71%	511	1.80%
2004	11,754	48.19%	12,334	50.57%	302	1.24%
2000	10,053	47.71%	10,228	48.55%	788	3.74%
1996	7,460	38.57%	9,635	49.81%	2,247	11.62%
1992	7,706	34.97%	8,784	39.86%	5,547	25.17%
1988	10,362	56.07%	7,960	43.07%	160	0.87%
1984	12,215	65.00%	6,435	34.24%	143	0.76%
1980	10,407	50.24%	7,293	35.21%	3,015	14.55%
1976	10,577	57.66%	7,281	39.69%	487	2.65%
1972	9,682	55.47%	7,446	42.66%	326	1.87%
1968	7,111	57.37%	4,450	35.90%	835	6.74%
1964	4,672	39.84%	7,040	60.03%	15	0.13%
1960	7,880	63.88%	4,431	35.92%	24	0.19%
1956	8,415	72.41%	3,183	27.39%	23	0.20%
1952	8,222	73.54%	2,881	25.77%	77	0.69%
1948	5,485	67.23%	2,487	30.49%	186	2.28%
1944	6,356	71.02%	2,522	28.18%	71	0.79%
1940	7,019	70.96%	2,828	28.59%	44	0.44%
1936	4,051	46.79%	3,871	44.71%	736	8.50%
1932	4,211	48.71%	4,272	49.42%	162	1.87%
1928	4,926	73.13%	1,762	26.16%	48	0.71%
1924	5,245	77.08%	1,208	17.75%	352	5.17%
1920	5,089	73.82%	1,627	23.60%	178	2.58%
1916	2,700	53.91%	2,143	42.79%	165	3.29%
1912	1,417	29.71%	1,389	29.13%	1,963	41.16%
1908	3,171	63.18%	1,658	33.03%	190	3.79%
1904	3,547	70.97%	1,321	26.43%	130	2.60%
1900	2,969	58.64%	1,996	39.42%	98	1.94%
1896	2,424	46.71%	2,679	51.63%	86	1.66%
1892	1,859	45.42%	1,762	43.05%	472	11.53%
1888	2,154	51.46%	1,841	43.98%	191	4.56%
1884	1,617	48.78%	1,610	48.57%	88	2.65%

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.

• Clare (part)
• Mount Pleasant (county seat)

• Lake Isabella
• Rosebush
• Shepherd

• Union Charter Township

• Beal City
• Loomis
• Weidman
• Winn

• Isabella Indian Reservation

The Gratiot–Isabella Regional Education Service District, based in Ithaca, services the students in the county. The intermediate school district offers regional special education services, early education programs, and technical career pathways for students of its districts.

Isabella County is served by the following regular public school districts:

• Beal City Public Schools
• Mt. Pleasant City School District
• Shepherd Public Schools

The county also has the following independent charter districts:

• Flextech High School - Shepherd
• Renaissance Public School Academy

Isabella County has the following private schools:

• Sacred Heart Academy (Roman Catholic)
• Saginaw Chippewa Academy (Nonsectarian)
• St. Joseph the Worker School (Roman Catholic)
• White Pine Montessori Children's Center (Montessori method)

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

• "Bibliography on Isabella County". Clarke Historical Library, Central Michigan University.
• "Isabella County official website". Isabella County, Michigan.

43°39′N 84°50′W / 43.65°N 84.84°W / 43.65; -84.84