Keithsburg is a city in Mercer County, Illinois, United States, on the Mississippi River. The population was 550 at the 2020 census, down from 609 in 2010. It was named for Robert Keith, a pioneer settler. Due to a flood in 1993, there isn't much to do in Keithsburg. Some of the things that are still in use today include, a bar/restaurant named “The Eagles Nest”, and one or two playgrounds.