Monkton is an unincorporated community in northern Baltimore County, Maryland, United States. It has a population of approximately 4,856 people. The community is 35 square miles (91 km2) in area, with approximately 138 inhabitants per square mile (53/km2). As an unincorporated area, Monkton has no legally defined boundaries, and its ZIP code (21111) includes a portion of adjacent Harford County.