Rosiclare is a city in Hardin County, Illinois, along the Ohio River. The population was 1,160 at the 2010 census, down from 1,213 at the 2000 census.

Hardin County is a county located in the U.S. state of Illinois. According to the 2020 census, it has a population of 3,649, making it the least populous county in Illinois. Its county seat is Elizabethtown. Hardin County is located in the part of the state known as Little Egypt. Hardin County was named for Hardin County, Kentucky, which was named in honor of Colonel John Hardin, an officer in the American Revolutionary War and the Northwest Indian War.