Gem County is a county in the U.S. state of Idaho. As of the 2020 census, the population was 19,123. The county seat and largest city is Emmett.

Emmett is a city in Gem County, Idaho, United States. The population was 6,557 at the 2010 census, up from 5,490 in 2000. It is the county seat and the only city in the county. Emmett is part of the Boise−Nampa, Idaho Metropolitan Statistical Area.