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 major cities in New Castle County, Delaware, are anchored by the largest city, Wilmington, followed by Newark and Middletown. Other notable incorporated municipalities include New Castle, Elsmere, Delaware City, and Newport, with significant unincorporated suburban communities like Bear and Hockessin.