St. Leonard is a census-designated place (CDP) in Calvert County, Maryland, United States. The population was 742 at the 2010 census.
St. Leonard has a small central business district with several small shops, gas stations, and an independent grocery store originally owned and operated by former Calvert County Commissioner Patrick Buehler. The town has a volunteer fire department which has hosted numerous high-profile musical acts, including Lynyrd Skynyrd, Alan Jackson, and Hootie and the Blowfish at an outdoor pavilion adjacent to the fire department. Notable places of interest near St. Leonard include Flag Ponds Nature Park, a nature preserve south of Long Beach along Chesapeake Bay, and Jefferson Patterson State Park 7 miles (11 km) south of town, home to an annual Celtic festival, to Maryland's state archaeological facility, and the site of several key naval battles fought in the Patuxent River during the War of 1812.