The interior of much of the county is hilly to varying degrees, with forests and agricultural fields.
St. Mary's County borders Virginia across the Potomac River,[REF] St. Mary's County waters are also bordered by Virginia's territorial waters in Potomac tributary mouths on the Virginia side,[REF] tidal interface zones[REF] and the Chesapeake Bay[REF] (water rights in all of these areas are still sometimes disputed) [REF].