Don't miss out on the 2nd fastest growing County in Missouri - Jefferson County, the southern most county in the Metro St Louis area is a rural community that is fast becoming an urban area.  With a population of 198,099, per the 2000 census.  The county seat is in Hillsboro. Cities and towns in Jefferson County that are a part of the Metro St Louis area include: Arnold*, Barnhart, Big River, Byrnes Mill*, Cedar Hill, Cedar Hill Lakes*, Central, Crystal City*, DeSoto*, Festus*, Herculaneum*, High Ridge, Hillsboro*, Horine, House Springs, Imperial, Joachim, Kimmswick*, Meramec, Murphy, Olympian Village*, Parkdale*, Pevely*, Plattin, Riverview, Rock, Scotsdale*, Valle, Windsor, (out of these, only the towns that are * are incorporated). Much of Jefferson County features rolling hills and farm land.