Logan County is a county located in the U.S. state of Illinois. According to the 2020 census, it had a population of 27,987. Its county seat is Lincoln.

Lincoln is a city in Logan County, Illinois, United States. First settled in the 1830s, it is the only town in the U.S. that was named for Abraham Lincoln before he became president; he practiced law there from 1847 to 1859. Lincoln is home to two prisons. It is also the home of the world's largest covered wagon and numerous other historical sites along the Route 66 corridor.