New Castle County, Delaware

New Castle County population, land area and income

New Castle County had 588,093 residents in the Census Vintage 2024 estimate, on 426.3 square miles of land. It is the most populous of Delaware's 3 county-equivalents. That works out to 1,379.4 people per square mile, 14.3 times the US average of 96.3, and in the top tenth nationally.

The median county-equivalent in Delaware has 271,134 residents, so New Castle County is 2.2 times that size.

Its SAIPE 2023 median household income of $86,798 is in the top tenth among 3,143 counties with an estimate.

How New Castle County's population changed since 2020

New Castle County gained 17,136 residents between the July 2020 and July 2024 estimates, a rise of 3.0%. That ranks 3rd of 3 in Delaware for growth. The median Delaware county changed by +5.7%, and the state as a whole by +6.0%.

Since the April 2020 estimates base, New Castle County recorded 25,841 births and 23,725 deaths, a natural change of +2,116. Net international migration added +12,660 and net domestic migration, people moving to or from other US counties, came to +2,362. The largest single component was international migration, which added 12,660 people.

Where New Castle County is

The Census internal point of New Castle County is at 39.575900, -75.644100. It sits in UTM zone 18N. The map shades Delaware's 3 county-equivalents by population change from 2020 to 2024, darker for faster growth, with New Castle County outlined. Dots are towns of 1,000+ people with residents in it.

Towns in New Castle County

9 incorporated places of 1,000+ people have residents in New Castle County, 147,473 people together, or 25% of the county. Each figure counts only the part of the town inside New Castle County; towns marked "part" extend into another county. The largest is Wilmington with 73,176.

Counties bordering New Castle County

The Census 2024 county adjacency file lists 7 neighbors for New Castle County, including 6 across a state line. The most populous is Delaware County, PA, with 584,882 residents. Distances run between Census internal points in a straight line.

• PA

  Delaware County, PA

  584,882 people

  27 mi NNE

• PA

  Chester County, PA

  560,745 people

  28 mi NNW

• NJ

  Gloucester County, NJ

  311,783 people

  28 mi ENE

• Kent County

  192,690 people

  34 mi SSE

• MD

  Cecil County, MD

  106,305 people

  16 mi W

• NJ

  Salem County, NJ

  65,874 people

  15 mi E

• MD

  Kent County, MD

  19,557 people

  35 mi SW

Distance to Dover and the nearest big city

Dover is 29.7 miles SSE of New Castle County's internal point in a straight line. The nearest place of 100,000 or more is Philadelphia, PA (population 1,573,916), 40.4 miles away. The nearest place of 10,000 or more is Newark, DE (population 30,506), 9.3 miles away.

New Castle County FIPS code

The FIPS code of New Castle County is 10003: state code 10 for Delaware plus county code 003. Use it as text, with the leading zero, when joining Census, BLS, or CDC county tables. SAIPE lists its 2023 median household income as $86,798.