Moultrie County is a county in the U.S. state of Illinois. According to the 2020 United States Census, its population was 14,526. Its county seat is Sullivan. The name is pronounced as in "mole tree", unlike the pronunciation of its namesake, the South Carolinian Revolutionary War hero William Moultrie.

Moultrie County was formed in 1843 with areas taken from Shelby and Macon counties. It is named for South Carolina General, and later Governor, William Moultrie. General Moultrie defended Sullivan's Island, South Carolina from British attack in 1776. The site was later renamed Fort Moultrie. Nearby Jasper County was named for Sgt. William Jasper, another hero of the defense of Sullivan's Island.

The official flag of the county is the Moultrie Flag, which was flown over the new fortress on Sullivan's Island, when Moultrie defended it, and was designed by Moultrie. It went on to become iconic of liberty in the South.

When Abraham Kellar of Lovington, John Cook of Marrowbone, and John Fleming of Nelson proposed the formation of a new county from Macon, Shelby, and Coles counties, Macon gave up a strip of “worthless swamp” that is now among the most fertile land in the world, but Shelby and Coles voters refused to give up any land. Finally, Shelby County gave up some of its land to make a zig-zag border with Moultrie County.

• 
  Moultrie County at the time of its creation in 1843
• 
  The Moultrie Flag being raised by Sergeant William Jasper

According to the US Census Bureau, the county has a total area of 344 square miles (890 km), of which 336 square miles (870 km) is land and 8.5 square miles (22 km) (2.5%) is water.

Sullivan, Illinois
Climate chart (explanation)
J F M A M J J A S O N D     2     34 19     1.9     41 24     3.3     52 33     3.7     65 43     4     75 53     4.1     83 62     4     87 66     3.3     85 63     3.1     80 56     3.1     68 45     3.9     52 35     3     39 24 █ Average max. and min. temperatures in °F █ Precipitation totals in inches Source: The Weather Channel
Metric conversion J F M A M J J A S O N D     51     1 −7     48     5 −4     84     11 1     94     18 6     101     24 12     103     28 17     102     31 19     83     29 17     77     27 13     78     20 7     98     11 2     76     4 −4 █ Average max. and min. temperatures in °C █ Precipitation totals in mm

In recent years, average temperatures in the county seat of Sullivan have ranged from a low of 19 °F (−7 °C) in January to a high of 87 °F (31 °C) in July, although a record low of −26 °F (−32 °C) was recorded in January 1915 and a record high of 111 °F (44 °C) was recorded in July 1936. Average monthly precipitation ranged from 1.89 inches (48 mm) in February to 4.05 inches (103 mm) in June.

Historical population

Census	Pop.	Note	%±
1850	3,234		—
1860	6,385		97.4%
1870	10,385		62.6%
1880	13,699		31.9%
1890	14,481		5.7%
1900	15,224		5.1%
1910	14,630		−3.9%
1920	14,839		1.4%
1930	13,247		−10.7%
1940	13,477		1.7%
1950	13,171		−2.3%
1960	13,635		3.5%
1970	13,263		−2.7%
1980	14,546		9.7%
1990	13,930		−4.2%
2000	14,287		2.6%
2010	14,846		3.9%
2020	14,526		−2.2%
2023 (est.)	14,342		−1.3%
US Decennial Census 1790-1960 1900-1990 1990-2000 2010-2013 2020

As of the 2010 United States Census, there were 14,846 people, 5,758 households, and 4,053 families living in the county. The population density was 44.2 inhabitants per square mile (17.1/km). There were 6,260 housing units at an average density of 18.6 per square mile (7.2/km). The racial makeup of the county was 98.5% white, 0.3% black or African American, 0.2% Asian, 0.2% American Indian, 0.2% from other races, and 0.6% from two or more races. Those of Hispanic or Latino origin made up 0.9% of the population. In terms of ancestry, 23.8% were German, 12.0% were Irish, 11.4% were American, and 10.9% were English.

Of the 5,758 households, 31.8% had children under the age of 18 living with them, 57.6% were married couples living together, 8.9% had a female householder with no husband present, 29.6% were non-families, and 25.5% of all households were made up of individuals. The average household size was 2.51 and the average family size was 3.01. The median age was 40.3 years.

The median income for a household in the county was $46,364 and the median income for a family was $54,494. Males had a median income of $42,581 versus $26,799 for females. The per capita income for the county was $22,954. About 6.2% of families and 11.0% of the population were below the poverty line, including 17.2% of those under age 18 and 6.7% of those age 65 or over.

• Sullivan (seat)

Moultrie County is served by three school districts.

• Sullivan Community Unit School District 300
• Okaw Valley Community Unit School District 302
• Arthur-Lovington/Atwood-Hammond Community Unit School District 305

Moultrie County voters have voted for the Republican Party candidate in eight of the last ten national election campaigns.

United States presidential election results for Moultrie County, Illinois

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	4,816	73.77%	1,615	24.74%	97	1.49%
2020	4,964	73.48%	1,662	24.60%	130	1.92%
2016	4,455	70.91%	1,481	23.57%	347	5.52%
2012	3,784	62.29%	2,144	35.29%	147	2.42%
2008	3,471	55.33%	2,668	42.53%	134	2.14%
2004	4,028	62.30%	2,388	36.93%	50	0.77%
2000	3,058	53.41%	2,529	44.17%	138	2.41%
1996	2,199	40.34%	2,629	48.23%	623	11.43%
1992	2,065	31.94%	3,056	47.27%	1,344	20.79%
1988	3,167	50.98%	3,013	48.50%	32	0.52%
1984	3,593	59.17%	2,458	40.48%	21	0.35%
1980	3,495	56.73%	2,332	37.85%	334	5.42%
1976	2,803	45.44%	3,332	54.01%	34	0.55%
1972	3,143	57.07%	2,350	42.67%	14	0.25%
1968	3,094	50.50%	2,447	39.94%	586	9.56%
1964	2,493	40.04%	3,733	59.96%	0	0.00%
1960	3,752	54.93%	3,079	45.07%	0	0.00%
1956	3,756	57.65%	2,751	42.23%	8	0.12%
1952	3,880	59.12%	2,675	40.76%	8	0.12%
1948	3,043	49.39%	3,037	49.29%	81	1.31%
1944	3,180	52.31%	2,853	46.93%	46	0.76%
1940	3,636	49.32%	3,696	50.13%	41	0.56%
1936	3,074	42.41%	4,110	56.70%	65	0.90%
1932	2,353	35.40%	4,219	63.48%	74	1.11%
1928	3,310	60.31%	2,168	39.50%	10	0.18%
1924	3,001	53.10%	2,403	42.52%	248	4.39%
1920	3,279	55.76%	2,513	42.73%	89	1.51%
1916	2,933	44.95%	3,370	51.65%	222	3.40%
1912	853	26.69%	1,501	46.96%	842	26.35%
1908	1,704	48.44%	1,695	48.18%	119	3.38%
1904	1,719	50.60%	1,470	43.27%	208	6.12%
1900	1,728	45.86%	1,975	52.42%	65	1.73%
1896	1,711	44.79%	2,077	54.37%	32	0.84%
1892	1,287	39.17%	1,670	50.82%	329	10.01%

• National Register of Historic Places listings in Moultrie County

39°38′N 88°37′W / 39.64°N 88.62°W / 39.64; -88.62