Missoula County is a county located in the State of Montana. As of the 2010 census, the population was 109,426, making it the second-most populous county in Montana. Its county seat and largest city is Missoula. The county was founded in 1860. The county shares a border with Sanders County, Lake County, and Flathead County to the north, Powell County to the east, Granite County and Ravalli County to the south, the state of Idaho to the southwest, and Mineral County to the west.
Missoula County comprises the Missoula, MT Metropolitan Statistical Area.