The population nearly doubled in the late 1920s, going from 9,500 residents in 1927 to 18,207 residents three years later. By 1940, after the subway opened, the population had increased to 32,500 residents. By this time, development had largely stopped due to World War II, and about 25 empty lots in Forest Hills Gardens were developed after the war. At the same time, the single-family houses in Forest Hills were being razed to create new apartment buildings. The land in Forest Hills Gardens was fully developed by the 1960s, but there would still be empty lots in Forest Hills itself until the mid-1990s.