New Castle County, Delaware
The most populous of Delaware's 3 counties.
CountyFIPS 10003
- 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.
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.
| Measure | Value | In Delaware | Nationally |
|---|---|---|---|
| Population | 588,026 | 1st of 3 | 121st of 3,144 |
| Land area | 426.3 sq mi | 3rd of 3 | 2,381st of 3,144 |
| Population density | 1,379 per sq mi | 1st of 3 | 119th of 3,144 |
| Median household income | $91,166 | 1st of 3 | 278th of 3,143 |
Full data for New Castle County
| Measure | Value | Source and vintage |
|---|---|---|
| Population | 588,026 | Vintage 2025 Population Estimates |
| Population in 2020 | 570,941 | Vintage 2025 Population Estimates |
| 2020 estimates base? | 570,722 | Vintage 2025 Population Estimates |
| Land area | 426.3 sq mi | 2025 Gazetteer Files |
| Water area | 67.7 sq mi | 2025 Gazetteer Files |
| Total area | 494 sq mi | 2025 Gazetteer Files |
| Population density? | 1,379 per sq mi | Computed: Vintage 2025 estimates divided by 2025 Gazetteer land area |
| Median household income | $91,166 | American Community Survey 2020-2024 5-Year Estimates |
| Median home value | $352,200 | American Community Survey 2020-2024 5-Year Estimates |
| Median age | 39.3 | American Community Survey 2020-2024 5-Year Estimates |
| Households | 224,173 | American Community Survey 2020-2024 5-Year Estimates |
| Housing units | 236,079 | American 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 area | State | Shared border | Population |
|---|---|---|---|
| Salem County | New Jersey | 38 mi | 66,280 |
| Cecil County | Maryland | 24 mi | 107,131 |
| Kent County | Delaware | 22 mi | 194,786 |
| Chester County | Pennsylvania | 15 mi | 557,116 |
| Delaware County | Pennsylvania | 9.4 mi | 580,937 |
| Kent County | Maryland | 5.6 mi | 19,565 |
| Gloucester County | New Jersey | 0.6 mi | 312,638 |
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.
- Kent County
- New Castle County
- Sussex County
Data on this page last rebuilt 30 August 2026. How these figures are produced.