St. Louis is a two-state map. St. Louis City is independent of St. Louis County, so search language changes between them, and Clayton, Kirkwood, Webster Groves and Chesterfield each hold their own identities. St. Charles sits across the Missouri River.
On the other bank of the Mississippi, Belleville and the Metro East towns fall under Illinois rules and different local governments. Older brick housing in the city and inner suburbs, county lots further out, and Metro East suburban housing all produce different search wording.
Listing searches mostly go to Zillow, MARIS and Realtor.com. Missouri and Illinois broker licenses apply to property work, and trades follow state, county and city licensing rules, so a page should be clear about which side it serves.
HeyLead handles the marketing, and the licenses stay yours.