Major highways

• Montana Highway 16
• Montana Highway 23
• Montana Highway 200

Adjacent counties

2020 census

As of the 2020 census, there were 11,491 people living in the county.^{[citation needed]}

2010 census

As of the 2010 census, there were 9,746 people, 4,167 households, and 2,698 families in the county. The population density was 4.7 inhabitants per square mile (1.8/km²). There were 4,550 housing units at an average density of 2.2 per square mile (0.85/km²). The racial makeup of the county was 95.0% white, 1.7% American Indian, 0.2% Asian, 0.1% black or African American, 0.8% from other races, and 2.1% from two or more races. Those of Hispanic or Latino origin made up 3.0% of the population. In terms of ancestry, 37.8% were German, 23.1% were Norwegian, 13.0% were Irish, 8.7% were American, and 6.5% were English.

Of the 4,167 households, 28.9% had children under the age of 18 living with them, 51.9% were married couples living together, 7.6% had a female householder with no husband present, 35.3% were non-families, and 29.8% of all households were made up of individuals. The average household size was 2.33 and the average family size was 2.88. The median age was 41.3 years.

The median income for a household in the county was $52,516 and the median income for a family was $60,236. Males had a median income of $44,788 versus $23,135 for females. The per capita income for the county was $26,888. About 10.2% of families and 13.5% of the population were below the poverty line, including 16.6% of those under age 18 and 14.4% of those age 65 or over.

City

• Sidney (county seat)

Town

• Fairview

Census-designated places

• Crane
• Fox Lake
• Savage

Other unincorporated places