northwestern suburban area of Washington, D.C. (Washington), in Montgomery county, Maryland, U.S. It is not an incorporated entity but a group of communities (Bethesda and several associated with Chevy Chase) that prior to 1949 were governed by county commissioners and thereafter came mostly under the jurisdiction of chartered, popularly elected councils. The district takes its name from the Bethesda Presbyterian Church, built in 1820 on the Georgetown-Frederick Pike (Old National Road), and Chevy Chase village (incorporated 1910). Residential development greatly increased after World War II. Government facilities accounted for much of the expansion, which began in 1937 with the National Cancer Institute, followed by the National Institutes of Health, the National Naval Medical Center (1942), and various research institutes. The National Library of Medicine there is the largest biomedical library in the world. Industrial facilities are oriented toward federal agencies. Pop. (1990) Bethesda, 62,936; Chevy Chase, 8,559; (2000) Bethesda, 55,277; Chevy Chase, 9,381.