Maryland Route 5 is a 74.34-mile (119.64 km) long state highway that runs north–south in the U.S. state of Maryland. The highway runs from Point Lookout in St. Mary's County north to the Washington, D.C. border in Suitland, Prince George's County. MD 5 begins as two-lane undivided Point Lookout Road which runs from Point Lookout to an intersection with MD 235 in the northern part of St. Mary's County. Point Lookout Road passes through rural areas as well as the county seat of Leonardtown. After the MD 235 intersection, the route becomes four-lane divided Three Notch Road and continues into Charles County, where it becomes Leonardtown Road. Here, the route bypasses Hughesville and continues north toward the Waldorf area, which it bypasses to the east on Mattawoman Beantown Road. The route merges onto U.S. Route 301 and enters Prince George's County, splitting from US 301 at an interchange in Brandywine. From here, MD 5 continues north on Branch Avenue, running through suburban areas, before becoming a freeway as it passes Andrews Air Force Base and has an interchange with Interstate 95 (I-95)/I-495. Past the Capital Beltway, the route runs through suburban areas of Hillcrest Heights and Suitland before reaching the Washington, D.C. border, where Branch Avenue SE continues, crossing Pennsylvania Avenue SE and eventually terminating at Randle Circle.

St. Mary's County, established in 1637, is a county located in the U.S. state of Maryland. As of the 2020 census, the population was 113,777. Its county seat is Leonardtown. The name is in honor of Mary, the mother of Jesus. St. Mary's County comprises the California-Lexington Park, Maryland Metropolitan Statistical Area, which also is included in the Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area. It is part of the Southern Maryland region. The county was the home to the first Maryland Colony, and the first capital of the Colony of Maryland. Settled by English Catholics, it is considered to be the birthplace of religious freedom in North America, at a time when the British colonies were settled primarily by Protestants. The county is home to the Patuxent River Naval Air Station and St. Mary's College of Maryland. Traditionally, St. Mary's County has been known for its unique and historic culture of Chesapeake Bay tidewater farming, fishing, and crabbing communities. But with the advent of the military bases, growth of an extensive defense contractor presence, and the growth of St. Mary's College of Maryland, as well as increasing numbers of long-distance Washington, D.C. commuters, it has been undergoing a decades-long transformation which has seen the county's population double since 1970.