New Castle County is the northernmost of the three counties of the U.S. state of Delaware. As of the 2020 census, the population was 570,719, making it the most populous county in Delaware, with nearly 60% of the state's population of 989,948. The county seat is Wilmington, which is also the state's most populous city.
Country: United States
State: Delaware
Founded: August 8, 1673
Named for: William Cavendish, 1st Duke of Newcastle
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