Sale of good will–Seller’s agreement with buyer to refrain from carrying on similar business, validity
Any person who sells the good will of a business may agree with the buyer to refrain from carrying on a similar business within a specified county, city, or other specified area, as long as the buyer or person deriving title to the good will from the seller carries on a like business within the specified geographical area.
See https://sdlegislature.gov/Statutes/Codified_Laws/DisplayStatute.aspx?Type=Statute&Statute=53-9