Fallon County is a county located in the U.S. state of Montana. As of the 2020 census, the population was 3,049. Its county seat is Baker. The county was created in 1913 from a portion of Custer County. It is named for Benjamin O'Fallon, a nephew of Captain William Clark and an Indian agent for the upper Missouri region from 1823 to 1827.

According to the United States Census Bureau, the county has a total area of 1,623 square miles (4,200 km), of which 1,621 square miles (4,200 km) is land and 2.3 square miles (6.0 km) (0.1%) is water.

United States presidential election results for Fallon County, Montana

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	1,375	87.30%	172	10.92%	28	1.78%
2016	1,279	86.19%	154	10.38%	51	3.44%
2012	1,128	80.23%	237	16.86%	41	2.92%
2008	1,064	74.25%	318	22.19%	51	3.56%
2004	1,178	79.01%	289	19.38%	24	1.61%
2000	1,061	77.50%	256	18.70%	52	3.80%
1996	778	51.32%	452	29.82%	286	18.87%
1992	731	45.46%	446	27.74%	431	26.80%
1988	1,002	61.25%	612	37.41%	22	1.34%
1984	1,237	67.63%	569	31.11%	23	1.26%
1980	1,286	66.98%	512	26.67%	122	6.35%
1976	934	51.98%	847	47.13%	16	0.89%
1972	1,034	64.46%	531	33.10%	39	2.43%
1968	990	63.26%	477	30.48%	98	6.26%
1964	827	51.85%	765	47.96%	3	0.19%
1960	918	60.55%	597	39.38%	1	0.07%
1956	967	61.24%	612	38.76%	0	0.00%
1952	1,046	70.01%	440	29.45%	8	0.54%
1948	678	51.02%	623	46.88%	28	2.11%
1944	870	63.46%	494	36.03%	7	0.51%
1940	925	56.96%	686	42.24%	13	0.80%
1936	598	36.00%	1,015	61.11%	48	2.89%
1932	690	39.79%	973	56.11%	71	4.09%
1928	1,036	69.07%	454	30.27%	10	0.67%
1924	731	55.63%	220	16.74%	363	27.63%
1920	1,064	71.36%	381	25.55%	46	3.09%
1916	1,169	37.54%	1,845	59.25%	100	3.21%

Historical population

Census	Pop.	Note	%±
1920	4,548		—
1930	4,568		0.4%
1940	3,719		−18.6%
1950	3,660		−1.6%
1960	3,997		9.2%
1970	4,050		1.3%
1980	3,763		−7.1%
1990	3,103		−17.5%
2000	2,837		−8.6%
2010	2,890		1.9%
2020	3,049		5.5%
2022 (est.)	3,011		−1.2%
U.S. Decennial Census 1790–1960, 1900–1990, 1990–2000, 2010–2020

As of the 2020 census, there were 3,049 people living in the county.

As of the 2010 census, there were 2,890 people, 1,233 households, and 810 families living in the county. The population density was 1.8 inhabitants per square mile (0.69/km). There were 1,470 housing units at an average density of 0.9 units per square mile (0.35 units/km). The racial makeup of the county was 97.4% white, 0.6% Asian, 0.4% American Indian, 0.1% Pacific islander, 0.1% black or African American, 0.2% from other races, and 1.3% from two or more races. Those of Hispanic or Latino origin made up 1.2% of the population. In terms of ancestry, 53.0% were German, 24.8% were Irish, 12.1% were Norwegian, 10.6% were English, 5.3% were Scotch-Irish, and 0.4% were American.

Of the 1,233 households, 28.4% had children under the age of 18 living with them, 56.0% were married couples living together, 5.7% had a female householder with no husband present, 34.3% were non-families, and 30.1% of all households were made up of individuals. The average household size was 2.32 and the average family size was 2.88. The median age was 42.9 years.

The median income for a household in the county was $52,529 and the median income for a family was $64,500. Males had a median income of $41,570 versus $30,000 for females. The per capita income for the county was $26,819. About 5.7% of families and 8.5% of the population were below the poverty line, including 16.3% of those under age 18 and 3.4% of those age 65 or over.

• U.S. Highway 12
• Montana Highway 7

The Baker Municipal Airport is southeast of Baker.

• Baker (county seat)

• Plevna

• List of lakes in Fallon County, Montana
• List of mountains in Fallon County, Montana
• National Register of Historic Places listings in Fallon County, Montana

• Fallon County, Montana Archived August 6, 2020, at the Wayback Machine

46°21′N 104°25′W / 46.35°N 104.41°W / 46.35; -104.41