Though the area has been settled for some time, Marathon is a relatively new city, incorporated in 1999. Its boundaries (according to both the city and a 2001 Rand McNally road map of the Keys) extend from the east end of the Seven Mile Bridge (Mile Marker 47) to the west end of Tom's Harbor Bridge (Mile Marker 61), excluding that portion of the area within the city limits of Key Colony Beach. Among the islands within the city limits are Boot Key, Knight's Key, Hog Key, Vaca Key, Stirrup Key, Crawl Key, Little Crawl Key, East and West Sister’s Island, Deer Key, Fat Deer Key (excluding the portion in Key Colony Beach), Long Point Key, and Grassy Key.