Mount Sterling is a city in and the county seat of Brown County, Illinois, United States. The population was 2,006 at the 2020 census.

Foodservice distributor Dot Foods is based in Mount Sterling.

Mount Sterling was organized in 1854. It did not have a courthouse until 1868, although it was designated the county seat from when the county was organized.

Mount Sterling was one of several Illinois towns that publicly competed for a new state prison in one of the state's prison sweepstakes competitions. During the 1987 competition, the town of Flora famously produced the "Is We Is or Is We Isn't/Gonna Get Ourselves A Prison" video. Ultimately, Mount Sterling won the 1987 competition and the state constructed the Western Illinois Correctional Center along State Highway 99 a mile south of town. In 1989 immediately prior to opening, the prison hosted a "Spend a night in prison" event for state and local dignitaries and prominent business-owners, an event that ultimately soured some of its participants on the economic value of prisons to small town economies.

According to the 2021 census gazetteer files, Mount Sterling has a total area of 1.11 square miles (2.87 km), all land.

Historical population

Census	Pop.	Note	%±
1850	556		—
1870	1,352		—
1880	1,445		6.9%
1890	1,655		14.5%
1900	1,960		18.4%
1910	1,986		1.3%
1920	1,932		−2.7%
1930	1,724		−10.8%
1940	2,140		24.1%
1950	2,246		5.0%
1960	2,262		0.7%
1970	2,182		−3.5%
1980	2,186		0.2%
1990	1,922		−12.1%
2000	2,070		7.7%
2010	2,025		−2.2%
2020	2,006		−0.9%
U.S. Decennial Census

As of the 2020 census there were 2,006 people, 956 households, and 481 families residing in the city. The population density was 1,810.47 inhabitants per square mile (699.03/km). There were 989 housing units at an average density of 892.60 per square mile (344.63/km). The racial makeup of the city was 93.47% White, 1.25% African American, 0.25% Native American, 0.25% Asian, 0.30% from other races, and 4.49% from two or more races. Hispanic or Latino people of any race were 1.55% of the population.

There were 956 households, out of which 27.0% had children under the age of 18 living with them, 35.46% were married couples living together, 13.60% had a female householder with no husband present, and 49.69% were non-families. 42.26% of all households were made up of individuals, and 14.12% had someone living alone who was 65 years of age or older. The average household size was 3.16 and the average family size was 2.24.

The city's age distribution consisted of 27.8% under the age of 18, 7.6% from 18 to 24, 28.1% from 25 to 44, 22.3% from 45 to 64, and 14.2% who were 65 years of age or older. The median age was 35.0 years. For every 100 females, there were 106.7 males. For every 100 females age 18 and over, there were 86.0 males.

The median income for a household in the city was $45,536, and the median income for a family was $73,693. Males had a median income of $43,019 versus $31,469 for females. The per capita income for the city was $24,433. About 6.4% of families and 12.8% of the population were below the poverty line, including 12.6% of those under age 18 and 7.0% of those age 65 or over.

Mount Sterling is home to Brown County School District #1, which contains an elementary school, middle school, and high school. The sports teams for the district are referred to as the "Hornets".

• City of Mt. Sterling official website