County outline
Where New Castle County is located
Area breakdown
Land accounts for 86.3% of New Castle County’s measured area and water for 13.7%. Its combined area converts to 1,279.5 square kilometers or approximately 316,177 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 426.338 | 1,104.21 | 272,856.3 |
| Water | 67.689 | 175.314 | 43,321 |
| Total | 494.027 | 1,279.524 | 316,177.3 |
How New Castle County compares
By original Census land area, New Castle County ranks #3 of 3 in Delaware and #2381 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.727 times the Delaware county-equivalent median of 586.1 square miles. It accounts for 21.9% of the combined county land area in the state.
See the complete Delaware ranking · What counts as a county equivalent?
Population and density of New Castle County
The Census Bureau estimates that 588,026 people lived in New Castle County on July 1, 2025. That ranks #121 of 3,222 county equivalents nationally and #1 of 3 in Delaware. Since the April 1, 2020 estimates base of 570,722, the population has grown by 17,304 (+3%), compared with +7.1% for Delaware as a whole.
With 426.3 square miles of land, that is 1,379 people per square mile (533 per km²), placing New Castle County #132 nationally for density and #1 in Delaware. The median county equivalent has 47 people per square mile; the Delaware median is 332. Put another way, there are about 0.464 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 570,941 | 572,097 | 575,913 | 581,067 | 586,014 | 588,026 |
| Change | — | +1,156 | +3,816 | +5,154 | +4,947 | +2,012 |
U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.
Cities and towns in New Castle County
15 incorporated places lie at least partly in New Castle County. Together they are home to 150,052 people (25.5%); the other 437,974 (74.5%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Wilmington city, with 73,512 residents in the county. By land, Middletown town is the largest at 13.5 mi². Among places with at least 1,000 residents in 2020, Middletown town grew fastest since then (+11.2%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Wilmington cityCounty seat | 73,512 | +3.7% | 10.9 |
| Newark city | 30,359 | −0.9% | 9.474 |
| Middletown town | 25,798 | +11.2% | 13.5 |
| Elsmere town | 6,196 | −0.5% | 0.987 |
| New Castle city | 5,726 | +3.3% | 3.478 |
| Townsend town | 2,985 | +9.6% | 1.12 |
| Delaware City city | 1,939 | +3% | 1.861 |
| Bellefonte town | 1,313 | +2.3% | 0.202 |
| Newport town | 906 | −0.4% | 0.467 |
| Arden village | 442 | +2.1% | 0.249 |
| Odessa town | 360 | −0.6% | 0.507 |
| Ardentown village | 257 | +2% | 0.234 |
| Ardencroft village | 232 | +1.8% | 0.089 |
| Smyrna townAlso in 1 other county | 27 | +12.5% | 6.473 |
| Clayton townAlso in 1 other county | 0 | — | 1.957 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside New Castle County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
New Castle County is a central county of the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD Metropolitan Statistical Area, in the Wilmington, DE-MD-NJ metropolitan division. Its 11 county equivalents have 6,329,118 residents on 4,603.2 square miles of land; New Castle County accounts for 9.3% of the land and 9.3% of the residents. By combined land it ranks #58 of 393 metropolitan areas, and #9 by population. It belongs to the Philadelphia-Reading-Camden, PA-NJ-DE-MD Combined Statistical Area.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| Philadelphia CountyPennsylvania | 1,574,281 | 134.3 |
| Montgomery CountyPennsylvania | 877,643 | 482.9 |
| Bucks CountyPennsylvania | 647,828 | 604.4 |
| New Castle County | 588,026 | 426.3 |
| Delaware CountyPennsylvania | 580,937 | 183.8 |
| Chester CountyPennsylvania | 557,116 | 750.6 |
| Camden CountyNew Jersey | 535,799 | 221.4 |
| Burlington CountyNew Jersey | 481,439 | 799.3 |
| Gloucester CountyNew Jersey | 312,638 | 322 |
| Cecil CountyMaryland | 107,131 | 346.3 |
| Salem CountyNew Jersey | 66,280 | 331.9 |
ZIP codes
32 ZIP Code Tabulation Areas have land in New Castle County; 29 of them have most of their land inside the county, and the others mainly cover neighboring areas.
1970119702197031970619707197091971019711197131971619717197201973019731197321973319734197351973619801198021980319804198051980619807198081980919810199381997721912
ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.
Counties bordering New Castle County
New Castle County shares a land border with 6 county equivalents, including 5 in Maryland, Pennsylvania, and New Jersey. It has more land than 4 of them. The largest neighbor is Chester County (750.6 mi²) and the smallest is Delaware County (183.8 mi²). Together with its neighbors, New Castle County forms a block of 2,901.9 mi² of land, of which it holds 14.7%.
| Bordering county equivalent | Land mi² | Size vs. New Castle | Compare |
|---|---|---|---|
| Chester CountyPennsylvania | 750.6 | 1.8× larger | Compare |
| Kent County | 586.1 | 1.4× larger | Compare |
| Cecil CountyMaryland | 346.3 | 1.2× smaller | Compare |
| Salem CountyNew Jersey | 331.9 | 1.3× smaller | Compare |
| Kent CountyMaryland | 276.9 | 1.5× smaller | Compare |
| Delaware CountyPennsylvania | 183.8 | 2.3× smaller | Compare |
How big is New Castle County compared with U.S. states?
New Castle County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 2.4 times as much. Delaware’s county land could hold about 4.6 areas the size of New Castle County.
Another way to picture it: the same land area would fill a square about 20.6 miles (33.2 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.
State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.
What stands out about New Castle County?
New Castle County has more land than 841 of the other 3,221 county equivalents in the dataset.
A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.
Does including water change its rank?
Using land plus water places New Castle County at #2,208 nationally by total area, 173 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.
Its water share is 13.7%, compared with a national county-equivalent median of 1.2% — 12.5 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.
Closest positions in the national land ranking
These entries sit immediately beside New Castle County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #2380 | Caldwell County, Missouri | 426.4 | Compare |
| #2381 | New Castle County, Delaware | 426.3 | This county |
| #2382 | Ashe County, North Carolina | 426.3 | Compare |
Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.
Representative coordinates
The Census internal point is 39.575915, -75.644132. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,104,210,679 m²; AWATER: 175,313,040 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is New Castle County?
New Castle County, Delaware has 426.3 square miles (1,104.2 km²) of land and 67.7 square miles of water, for a total area of 494 square miles. It ranks #2381 of 3,222 U.S. county equivalents by land area.
Is New Castle County the largest county in Delaware?
No. New Castle County ranks #3 of 3 in Delaware by land area. The largest is Sussex County, with 936.2 square miles of land.
What counties border New Castle County?
New Castle County shares a land border with Cecil County, Maryland, Kent County, Chester County, Pennsylvania, Delaware County, Pennsylvania, Kent County, Maryland, and Salem County, New Jersey.
What is the population of New Castle County?
The Census Bureau estimates New Castle County had 588,026 residents on July 1, 2025, ranking #121 of 3,222 county equivalents. That is 1,379 people per square mile of land.
What is the county seat of New Castle County?
The county seat of New Castle County is Wilmington.
What cities and towns are in New Castle County?
New Castle County has 15 incorporated places. The most populous five are Wilmington city, Newark city, Middletown town, Elsmere town, and New Castle city; 437,974 residents live outside any incorporated place.
Is New Castle County part of a metropolitan area?
Yes. It is a central county of the Philadelphia-Camden-Wilmington, PA-NJ-DE-MD Metropolitan Statistical Area, which has 11 county equivalents and 6,329,118 residents.
How many ZIP codes are in New Castle County?
32 ZIP Code Tabulation Areas have land in New Castle County, and 29 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does New Castle County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 2.4 times as much land.
How many acres of land are in New Castle County?
The land measurement converts to approximately 272,856 acres. Including water, total area is approximately 316,177 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.