Monrovia is an unincorporated community and census-designated place (CDP) in Frederick County, in theU.S. state of Maryland. As of the 2010 census it had a population of 416. The original unincorporated community of Monrovia is located along Maryland Route 75 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 and west to include nearly all of Ed McClain Road. According to theU.S. Census Bureau, the Monrovia CDP has a total area of 2.2 square miles (5.8 km2), all of it land.