 affton is a census-designated place (cdp) in st. louis county, missouri, united states, near st. louis. the population was 20,307 at the 2010 census. ==geography== affton is located at 38Â°33'4" north, 90Â°19'25" west (38.551052, -90.323614). according to the [[united states 
Census-designated_places_in_Missouri Census-designated_places_in_St._Louis_County,_Missouri