County Maps US

New Castle County, Delaware

The most populous of Delaware's 3 counties.

CountyFIPS 10003

Within Delaware
New Castle County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Wilmington, the county seat, located via the 2025 Census Gazetteer.

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Population
588,026
+17,085 (+3.0%) since 2020
Land area
426.3
square miles. A further 13.7% of the total area is water
Population density
1,379
people per square mile, computed rather than published
County seat
Wilmington
Seat of county government.
Established
1664
361 years ago
Largest city
Wilmington city
Population 73,512.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of New Castle County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of New Castle County, Delaware from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 452 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where New Castle County ranks

Position among the 3 counties of Delaware, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn DelawareNationally
Population588,0261st of 3121st of 3,144
Land area426.3 sq mi3rd of 32,381st of 3,144
Population density1,379 per sq mi1st of 3119th of 3,144
Median household income$91,1661st of 3278th of 3,143

Full data for New Castle County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population588,026Vintage 2025 Population Estimates
Population in 2020570,941Vintage 2025 Population Estimates
2020 estimates base?570,722Vintage 2025 Population Estimates
Land area426.3 sq mi2025 Gazetteer Files
Water area67.7 sq mi2025 Gazetteer Files
Total area494 sq mi2025 Gazetteer Files
Population density?1,379 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$91,166American Community Survey 2020-2024 5-Year Estimates
Median home value$352,200American Community Survey 2020-2024 5-Year Estimates
Median age39.3American Community Survey 2020-2024 5-Year Estimates
Households224,173American Community Survey 2020-2024 5-Year Estimates
Housing units236,079American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
+312
5,759 births, 5,447 deaths
Net migration
+1,655
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 7 areas bordering New Castle County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Salem CountyNew Jersey38 mi66,280
Cecil CountyMaryland24 mi107,131
Kent CountyDelaware22 mi194,786
Chester CountyPennsylvania15 mi557,116
Delaware CountyPennsylvania9.4 mi580,937
Kent CountyMaryland5.6 mi19,565
Gloucester CountyNew Jersey0.6 mi312,638

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

Side by side

All 3 counties of Delaware

Open the interactive Delaware county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.