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 , of which is land and (0.1%) is water.
Fallon County is a heavily Republican county, like most in eastern Montana, having supported the Republican presidential candidate in every election since 1936.
As of the 2020 census, the county had a population of 3,049. Of the residents, 27.6% were under the age of 18 and 17.7% were 65 years of age or older; the median age was 39.0 years. For every 100 females there were 99.2 males, and for every 100 females age 18 and over there were 101.2 males. 0.0% of residents lived in urban areas and 100.0% lived in rural areas.
The racial makeup of the county was 94.7% White, 0.2% Black or African American, 0.9% American Indian and Alaska Native, 0.2% Asian, 0.4% from some other race, and 3.5% from two or more races. Hispanic or Latino residents of any race comprised 2.1% of the population.
There were 1,213 households in the county, of which 31.3% had children under the age of 18 living with them and 19.7% had a female householder with no spouse or partner present. About 29.0% of all households were made up of individuals and 13.9% had someone living alone who was 65 years of age or older.
There were 1,526 housing units, of which 20.5% were vacant. Among occupied housing units, 76.3% were owner-occupied and 23.7% were renter-occupied. The homeowner vacancy rate was 2.3% and the rental vacancy rate was 24.9%.
As of the 2010 census, there were 2,890 people, 1,233 households, and 810 families living in the county. The population density was . There were 1,470 housing units at an average density of . 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.
The Baker Municipal Airport is southeast of Baker.