In urban planning, a central city (also known as a historic core city) refers to the municipality within a present metropolitan area that held the largest population in 1940. This designation was used to identify the historical center of growth before the expansion of suburban employment patterns changed the structure of metropolitan areas.
The United States Census Bureau has retired the term central city and replaced it with "principal city." While a principal city can include both historic core cities and post-WWII cities, a central city must not be confused with the "core" of a metropolitan area. The latter is defined by the census bureau as any urban area with a population exceeding 50,000.