Jersey County, Illinois
Jersey County is a county located in the U.S. state of Illinois. At the 2020 census, it had a population of 21,512. The county seat and largest community is Jerseyville, with a population of 8,337 in 2010. The county's smallest incorporated community is Otterville, with a population of 87.
Jersey County is included in the St. Louis, MO-IL Metropolitan Statistical Area.