Gem County is a county in the U.S. state of Idaho. As of the 2010 census, the population was 16,719. The county seat and largest city is Emmett. Gem County is part of the Boise, ID Metropolitan Statistical Area. Gem County is home to the Idaho ground squirrel.
According to the U.S. Census Bureau, the county has a total area of 566 square miles (1,470 km²), of which 561 square miles (1,450 km²) is land and 4.8 square miles (12 km²) (0.8%) is water. It is the fifth-smallest county in Idaho by area.
As of the 2010 United States Census, there were 16,719 people, 6,495 households, and 4,611 families residing in the county. The population density was 29.8 inhabitants per square mile (11.5/km²). There were 7,099 housing units at an average density of 12.7 per square mile (4.9/km²). The racial makeup of the county was 93.4% white, 0.6% American Indian, 0.5% Asian, 0.1% Pacific islander, 0.1% black or African American, 3.1% from other races, and 2.2% from two or more races. Those of Hispanic or Latino origin made up 8.0% of the population. In terms of ancestry, 23.2% were German, 19.2% were English, 15.8% were American, and 12.3% were Irish.
Of the 6,495 households, 30.6% had children under the age of 18 living with them, 56.9% were married couples living together, 9.3% had a female householder with no husband present, 29.0% were non-families, and 24.3% of all households were made up of individuals. The average household size was 2.55 and the average family size was 3.01. The median age was 42.9 years.