actually, many areas of the County use St. Louis as the "city address" but are considered part of a different municipality; I believe zip codes are more representative of locale, such as 63135, 63136 & 63145 are considered "Ferguson"
maybe this link could be helpful (it is to me)
http://www.zipmap.net/Missouri/St._Louis_County/Ferguson.htm
and this link is AWESOME: http://www.maptechnica.com/us-city-boundary-map/city/Ferguson/state/MO/cityid/2923986
gonna have to book mark it
Where I live, I am in 1 municipality, many have me in a different municipality because that's where the post office is and I commonly use St. Louis because that is what people are more familiar with.