Carter County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 1,415, making it the seventh-least populous county in Montana. The county seat is Ekalaka.

Carter County was named for Thomas Henry Carter, the state's first congressman (representative in Congress from the Montana Territory, followed by first representative from the state of Montana to the US House of Representatives). Prior to settlement the land of Carter County was occupied by the Sioux tribe.

According to the United States Census Bureau, the county has a total area of 3,348 square miles (8,670 km), of which 3,341 square miles (8,650 km) is land and 7.5 square miles (19 km) (0.2%) is water.

Medicine Rocks State Park is located 14 miles north of Ekalaka. Weathering has given the rocks an unusual texture. The site was used by Indian hunting parties.

• Custer National Forest (part)

Historical population

Census	Pop.	Note	%±
1920	3,972		—
1930	4,136		4.1%
1940	3,280		−20.7%
1950	2,798		−14.7%
1960	2,493		−10.9%
1970	1,956		−21.5%
1980	1,799		−8.0%
1990	1,503		−16.5%
2000	1,360		−9.5%
2010	1,160		−14.7%
2020	1,415		22.0%
2022 (est.)	1,382		−2.3%
U.S. Decennial Census 1790–1960, 1900–1990, 1990–2000, 2010–2020

As of the 2020 census, there were 1,415 people and 628 households in Carter County. Of the population, 96.7% were White, 0.2% Black or African American, 1.0% Native American, 0.1% Asian, and 1.9% two or more races. 1.1% were Hispanic. 1.0% had a different primary language to English. The county was 50.1% female, 49.9% male.

The median household income was $48,000, $6,970 below the median of Montana. 61.7% of the population aged over 16 were in the civilian labor force. 14.7% of the population were classed as living in poverty. 2.4% of the population had a disability. 92.5% of the population graduated high school, with 20.2% obtaining a bachelor's degree or higher. 86.5% of households had a computer, with 77.9% having broadband access.

As of the 2010 census, there were 1,160 people, 532 households, and 354 families living in the county. The population density was 0.3 inhabitants per square mile (0.12/km). There were 810 housing units at an average density of 0.2 per square mile (0.077/km). The racial makeup of the county was 97.8% white, 0.9% American Indian, 0.1% black or African American, 0.1% Asian, 0.3% from other races, and 0.8% from two or more races. Those of Hispanic or Latino origin made up 0.7% of the population. In terms of ancestry, 41.5% were German, 19.6% were English, 18.8% were Norwegian, 12.3% were Irish, and 4.3% were American.

Of the 532 households, 20.5% had children under the age of 18 living with them, 59.4% were married couples living together, 4.3% had a female householder with no husband present, 33.5% were non-families, and 30.3% of all households were made up of individuals. The average household size was 2.16 and the average family size was 2.65. The median age was 50.2 years.

The median income for a household in the county was $35,703 and the median income for a family was $47,955. Males had a median income of $26,736 versus $18,274 for females. The per capita income for the county was $20,681. About 8.5% of families and 14.0% of the population were below the poverty line, including 20.4% of those under age 18 and 10.8% of those age 65 or over.

Carter County has voted for the Republican candidate in every presidential election since 1952, with Harry S. Truman being the last Democrat to carry the county.

United States presidential election results for Carter County, Montana

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	775	89.70%	74	8.56%	15	1.74%
2016	678	86.26%	70	8.91%	38	4.83%
2012	678	85.18%	96	12.06%	22	2.76%
2008	573	79.36%	111	15.37%	38	5.26%
2004	623	87.87%	76	10.72%	10	1.41%
2000	573	88.84%	53	8.22%	19	2.95%
1996	522	68.24%	150	19.61%	93	12.16%
1992	497	56.86%	154	17.62%	223	25.51%
1988	686	72.82%	242	25.69%	14	1.49%
1984	823	80.06%	194	18.87%	11	1.07%
1980	766	72.40%	237	22.40%	55	5.20%
1976	558	57.41%	344	35.39%	70	7.20%
1972	726	73.86%	218	22.18%	39	3.97%
1968	624	62.21%	269	26.82%	110	10.97%
1964	576	55.98%	453	44.02%	0	0.00%
1960	688	64.00%	383	35.63%	4	0.37%
1956	698	61.55%	436	38.45%	0	0.00%
1952	921	72.12%	351	27.49%	5	0.39%
1948	501	46.22%	568	52.40%	15	1.38%
1944	507	45.35%	610	54.56%	1	0.09%
1940	556	43.03%	734	56.81%	2	0.15%
1936	464	32.81%	929	65.70%	21	1.49%
1932	565	37.39%	915	60.56%	31	2.05%
1928	763	64.01%	420	35.23%	9	0.76%
1924	669	54.17%	283	22.91%	283	22.91%
1920	782	66.84%	342	29.23%	46	3.93%

• Ekalaka (county seat)

• Alzada

• Capitol

• List of lakes in Carter County, Montana
• List of mountains in Carter County, Montana

• CarterCountyMT.info

45°30′N 104°32′W / 45.50°N 104.54°W / 45.50; -104.54