New Castle County, Delaware

New Castle County
County of Delaware
Old New Castle Courthouse in New Castle (1936)
Flag Seal
Location within the U.S. state of Delaware
Delaware's location within the U.S.
Coordinates: 39°35′N 75°38′W / 39.58°N 75.64°W / 39.58; -75.64
Country	United States
State	Delaware
Founded	August 8, 1673
Named for	William Cavendish, 1st Duke of Newcastle
Seat	Wilmington
Largest city	Wilmington
Area
• Total	494 sq mi (1,280 km2)
• Land	426 sq mi (1,100 km2)
• Water	68 sq mi (180 km2)  13.8%
Population  (2020)
• Total	570,719[1]
• Density	1,339.72/sq mi (517.27/km2)
Time zone	UTC−5 (Eastern)
• Summer (DST)	UTC−4 (EDT)
Congressional district	At-large
Website	www.nccde.org

New Castle County is the northernmost of the three counties of the U.S. state of Delaware (New Castle, Kent, and Sussex). As of the 2020 census, the population was 570,719,^[2] making it the most populous county in Delaware, with nearly 60% of the state's population of 989,948. The county seat is Wilmington,^[3] which is also the state's most populous city.

New Castle County is included in the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD Metropolitan Statistical Area. The county is named after William Cavendish, 1st Duke of Newcastle (c. 1593–1676).

New Castle County has the highest population and population density of any Delaware county, and it is the smallest county in the state by area. It has more people than the other two counties, Kent and Sussex, combined. It is also the most economically developed of the three.