Many St. Charles County ZIP codes encompassing communities such as Cottleville, St. Peters, Weldon Spring, Defiance, Matson, O’Fallon, Lake St. Louis, and Dardenne Prairie are now included as part of the July 2025 RECA expansion.
These areas are located near historical uranium processing and transport routes from when the Downtown Mallinckrodt Uranium Processing facility moved to Weldon Spring.