Wikipedia says:
Bethesda is an urbanized, but unincorporated, area in southern Montgomery County, Maryland, just Northwest of Washington, D.C. It takes its name from a church located there, the Bethesda Presbyterian Church, built in 1820 and rebuilt in 1850, which in turn took its name from Jerusalem's Pool of Bethesda. (In Aramaic, beth hesda means "house of mercy".)
As an unincorporated area, Bethesda has no official boundaries. The United States Census Bureau defines a Census-Designated Place named Bethesda whose center is located at 38°59' North, 77°7' West. The United States Geological Survey has defined Bethesda as an area whose center is at slightly different from the Census Bureau's definition. Other definitions are used by the Bethesda Urban Planning District, the United States Postal Service, and other organizations. As of 2000, the Census-defined community had a total population of 55,277. (...) more....
by 
