Eureka is a city located in St. Louis County, Missouri, United States between the cities of St. Louis and Pacific along Interstate 44. It is a portion of the Greater St. Louis metro area. As of the 2010 census, the city had a population of 10,189. Since 1971, Eureka has been known as the home of the amusement park Six Flags St. Louis (formerly Six Flags Over Mid-America).