Jerome County is a county in the U.S. state of Idaho. As of the 2010 Census the county had a population of 22,374. The county seat and largest city is Jerome. The county was created by the Idaho Legislature on February 8, 1919, by a partition of Lincoln County. It was named after either Jerome Hill, a developer of the North Side Irrigation Project, his son-in-law Jerome Kuhn, or his grandson Jerome Kuhn, Jr.