|Mercer County Illinois Cities/Towns - Aledo (County Seat), Alexis, Eliza, Joy, Keithsburg, Matherville, Millersburg, New Boston, New Windsor, North Henderson, Seaton, Sherrard, Viola
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Mercer County is a county located in the U.S. state of Illinois. A 2016 population estimate shows was 15,730. Its county seat is Aledo.
Mercer County is named for Hugh Mercer (1726-1777), a physician and general during the American Revolution who died from wounds suffered at the Battle of Princeton.