Major highways

Transit

• Billings Metropolitan Transit
• Express Arrow
• Jefferson Lines

Adjacent counties

National protected areas

• Nez Perce National Historical Park (part)
• Pompeys Pillar National Monument

2020 census

As of the 2020 census there were 164,731 people living in the county.^{[citation needed]}

2010 census

As of the 2010 census, there were 147,972 people, 60,672 households, and 38,367 families residing in the county. The population density was 56.2 inhabitants per square mile (21.7/km²). There were 63,943 housing units at an average density of 24.3 per square mile (9.4/km²). The racial makeup of the county was 90.7% white, 4.0% American Indian, 0.6% black or African American, 0.6% Asian, 0.1% Pacific islander, 1.2% from other races, and 2.8% from two or more races. Those of Hispanic or Latino origin made up 4.7% of the population. In terms of ancestry, 32.4% were German, 14.0% were Irish, 11.3% were English, 10.0% were American, and 9.9% were Norwegian.

Of the 60,672 households, 30.5% had children under the age of 18 living with them, 48.0% were married couples living together, 10.5% had a female householder with no husband present, 36.8% were non-families, and 29.7% of all households were made up of individuals. The average household size was 2.38 and the average family size was 2.94. The median age was 38.3 years.

The median income for a household in the county was $48,641 and the median income for a family was $62,380. Males had a median income of $42,899 versus $30,403 for females. The per capita income for the county was $26,152. About 7.9% of families and 11.2% of the population were below the poverty line, including 15.6% of those under age 18 and 7.7% of those age 65 or over.

Cities

• Billings (county seat)
• Laurel

Town

• Broadview

Census-designated places

Other unincorporated communities

Ghost towns