"Baltimore County" is a county located in the northern part of the U.S. state of Maryland. In the United States Census of 2010, its population was 805,029. It is part of the Baltimore-Washington Metropolitan Area. Its county seat since 1854 has been Towson. The name of the county was derived from the barony of the Proprietor of the Maryland colony, Cæcilius Calvert, 2nd Baron Baltimore, and the town of "Baltimore" in County Longford, Ireland. Baltimore County no longer includes the City of Baltimore (Port established - 1706, Town founded - 1729, became "county seat" of Baltimore County - 1767, Incorporated as City - 1797, Annexed territory from County on west, north and east sides in 1818 and 1888, Left County to become an independent city in 1851, Last Annexation of land from Baltimore County on west, north, and east; and south from Anne Arundel County in 1919).
Much of Baltimore County is suburban in character, straddling the border between the Piedmont plateau and, in the southern regions of the county, the Atlantic coastal plain. Northern Baltimore County is primarily rural, with a landscape of rolling hills and deciduous forests characteristic of the Southeastern mixed forests.
Among the county's major employers are the Social Security Administration, which has its national headquarters in Woodlawn, and Black & Decker in Towson. During World War II, the Glenn L. Martin Company in Middle River had 53,000 employees manufacturing airplanes for the war effort and Bethlehem Steel had more than 30,000 workers at its sprawling Sparrows Point steel mill. Of the 410,100 persons in the county's workforce as of 2009, 25% are employed in the fields of education, health, and human services, and 10% in retailing, with less than 1% in agriculture.