Monrovia is an unincorporated community and census-designated place (CDP) in Frederick County, in the U.S. state of Maryland. As of the 2010 census it had a population of 416. The ZIP code for the area is 21770.
The original unincorporated community of Monrovia is located along Maryland Route 75 (Green Valley Road) in southeastern Frederick County, 1 mile (1.6 km) south of New Market. The Monrovia CDP extends south of the original Monrovia as far as Maryland Route 80 (Fingerboard Road) and west to include nearly all of Ed McClain Road. According to the U.S. Census Bureau, the Monrovia CDP has a total area of 2.2 square miles (5.8 km2), all land.
Monrovia is part of the Frederick County public school system. Children from the area attend Green Valley or Kemptown Elementary School, Windsor Knolls Middle School, and Urbana High School or Linganore High School, due to redistricting in the fall of 2010.
The two major roads in the area are Maryland Route 75 and Maryland Route 80. MD 80 leads west 4.5 miles (7.2 km) to Urbana and southeast 7 miles (11 km) to Damascus (via MD 27), while MD 75 leads north to New Market and south 5 miles (8 km) to Hyattstown.
Monrovia was the largest community in the New Market election district in 1880.