
New Castle County
- State:
- Delaware
- County Seat:
- Wilmington
New Castle County's estimated 2025 population is 585,268 with a growth rate of 0.57% in the past year according to the most recent United States census data. New Castle County is the largest county in Delaware. The 2010 population was 538,792 and has seen a growth of 8.63% since that time.