Frederick is a city in west-central Maryland, United States. It is the county seat of Frederick County, the largest county by area in the state of Maryland. Frederick is an outlying community of the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area, which is part of a greater Washington-Baltimore-Northern Virginia, DC-MD-VA-WV Combined Statistical Area. As of the 2008 U.S. Census Bureau estimates, the city has a total population of 59,213, making it the third-largest incorporated area in Maryland, behind Baltimore and Rockville. Frederick is home to Frederick Municipal Airport (FDK), which primarily accommodates general aviation traffic, and to the U.S. Army's Fort Detrick, the largest employer in the county. Frederick is also home to BP Solar, which is the second-largest employer in the county.