Wentzville is an exurb of St. Louis that is located in western St. Charles County, Missouri, United States. As of the 2023 U.S. Census Bureau estimates, the city had a total population of 47,497, making it the 15th largest city in Missouri. Wentzville has been the fastest growing city in Missouri, by percentage population increase, for two consecutive decades from 2000 to 2020. Wentzville is host to the St. Charles County Fair and the St. Louis Renaissance Festival, which are held at Rotary Park.