Eureka is a city and the county seat of Woodford County, Illinois. The population was 5,295 at the 2010 census. Eureka is part of the Peoria, Illinois Metropolitan Statistical Area. Eureka is a small community centered on the intersection of what is now U.S. 24 and Illinois 117. It is also one of the towns along the Ronald Reagan Trail, a series of roads that connect towns in central Illinois that were of importance to Reagan's early life.