Jefferson County is a county located in the U.S. state of Idaho. As of the 2020 Census, the county's population was 30,891. The county seat and largest city is Rigby. The county was established in 1913 and named after Thomas Jefferson, the third U.S. President. Jefferson County is part of the Idaho Falls, ID Metropolitan Statistical Area.

The Idaho Falls Metropolitan Statistical Area, as defined by the United States Census Bureau, is an area consisting of three counties in eastern Idaho, anchored by the city of Idaho Falls. As of the 2020 census, the MSA had a population of 154,855. It is just north of the Pocatello, Idaho Metropolitan Area.