New Castle County, Delaware

New Castle County is a county in Delaware, United States, the northernmost of the state’s three counties, about 33 miles southwest of Philadelphia. It had a population of 570,719 at the 2020 census, an estimated 588,026 by 2025, and covers 494 square miles (1,280 km2) centred near 39°35′N 75°38′W.

Wilmington is the county seat and the county’s largest city; its postal code is 19801. The county holds 4 cities, 6 incorporated towns, 3 incorporated villages and 13 census-designated places, and it runs on Eastern Time. Its FIPS code is 10003.

Towns & Villages in New Castle County

New Castle County has 26 named places on record: 13 incorporated cities, towns and villages with their own local government, and 13 census-designated places (CDPs) that the Census Bureau statistically tracks but that have no municipal government of their own. Delaware never adopted the civil-township system used further north, so there is no township column below.

Three names on this list are easy to confuse. Arden, Ardentown and Ardencroft are separate incorporated villages founded between 1900 and 1950 as neighboring Georgist single-tax communities, not one place under three names. Pike Creek and Pike Creek Valley are two adjoining but separately tabulated CDPs west of Wilmington — both take their name from the same stream. And Bellefonte, Delaware shares its name with the unrelated county seat of Centre County, Pennsylvania.

ZIP Codes

• 19801–19810, 19850, 19880, 19884–19886, 19890–19899 — Wilmington (the city alone uses more than a dozen ZIPs, including several PO-box-only codes)
• 19720–19721, 19726 — New Castle
• 19702, 19711–19718, 19725 — Newark
• 19706 — Delaware City
• 19709 — Middletown
• 19730 — Odessa
• 19733 — Saint Georges
• 19734 — Townsend
• 19804 — Newport
• 19805 — Elsmere
• 19810 — Arden, Ardentown and Ardencroft

Bear, Glasgow, Brookside, Hockessin, Pike Creek, Pike Creek Valley, Claymont, Wilmington Manor, North Star, Edgemoor, Greenville, Port Penn and Bellefonte have no ZIP code of their own; each is an unincorporated CDP or a small town whose mail is delivered under a neighboring city’s code.

Geography

New Castle County splits along the Fall Line, the boundary between the Piedmont plateau and the Atlantic Coastal Plain, which runs roughly through the Wilmington–Newark corridor. North of the line the land rises into rolling hills of schist and gneiss bedrock, drained by the Brandywine, White Clay and Red Clay creeks. South of the line the county flattens into coastal plain, cut by the Chesapeake and Delaware Canal, which links the Delaware River to Chesapeake Bay near Saint Georges and Delaware City. Of the county’s 494 square miles, 426 are land and 68 are water, most of it the tidal Delaware River forming the county’s eastern edge.

Chester County, Pennsylvania and Delaware County, Pennsylvania lie to the north and northeast, Gloucester County, New Jersey and Salem County, New Jersey lie east across the Delaware River, Kent County, Delaware lies south, and Cecil County, Maryland and Kent County, Maryland lie to the west and southwest. Delaware County, Gloucester County, Salem County, Cecil County and Kent County, Maryland all have their own pages on this site; Chester County, Pennsylvania and Kent County, Delaware do not.

Demographics

New Castle County had a population of 570,719 at the 2020 census, and the latest estimate puts the county near 588,026 residents by 2025. Wilmington and Newark are by far the two largest communities, together holding roughly 100,000 people. Median household income runs $91,166 (2024), above Delaware’s statewide figure of $82,174 (2023 ACS). Population density works out to about 1,340 people per square mile of land, the highest of Delaware’s three counties by a wide margin, reflecting the county’s position inside the Philadelphia metropolitan area.

Economy & Local Life

Health care and social assistance employs the most workers in the county, about 47,022 people, followed by retail trade at 31,752 and finance and insurance at 30,216. Wilmington’s finance sector traces to the 1981 Financial Center Development Act, which removed Delaware’s usury cap and drew national credit-card operations from Chase, Bank of America, Barclays and Capital One into the city. DuPont has anchored the county’s industrial base since 1802, when the company began manufacturing gunpowder along the Brandywine Creek; its corporate descendants Chemours and Corteva still keep headquarters in Wilmington. Newark is a university town built around the University of Delaware, and ChristianaCare’s Newark hospital campus is one of the county’s largest employers outside finance. Wilmington hosts the Clifford Brown Jazz Festival each June, named for the Wilmington-born jazz trumpeter, drawing musicians and audiences from across the region.

History

Swedish colonists built Fort Christina on the Christina River in 1638, the first permanent European settlement in the Delaware Valley, on the site that became Wilmington. New Castle itself served as William Penn’s landing place when he first set foot in America on 27 October 1682, after the town had been conveyed to him by the Duke of York; it later served as Delaware’s colonial capital before Dover took over in 1777. New Castle County traces its formal organization to 8 August 1673, and takes its name from William Cavendish, 1st Duke of Newcastle. The only Revolutionary War engagement fought on Delaware soil, the Battle of Cooch’s Bridge, took place near Newark on 3 September 1777, as Continental forces skirmished with British troops advancing toward Philadelphia.

Getting There

Interstate 95 crosses the county through Wilmington and Newark, with I-295 and I-495 forming a bypass loop around the city. US Routes 13, 40, 202 and 301 also cross the county.

• Philadelphia, Pennsylvania — about 33 miles northeast
• Baltimore, Maryland — southwest via I-95
• Dover, Delaware, the state capital — south via US 13 or Delaware Route 1

Philadelphia International Airport, north of Wilmington via I-95, is the nearest major commercial airport. New Castle Airport, in the city of New Castle, handles general aviation and occasional scheduled service. Amtrak and SEPTA regional trains stop at Wilmington’s Joseph R. Biden Jr. Railroad Station on the Northeast Corridor, connecting to Philadelphia, Baltimore and Washington.

Frequently Asked Questions

Where is New Castle County located?
It is Delaware’s northernmost county, about 33 miles southwest of Philadelphia, bordered by two Pennsylvania counties, two New Jersey counties across the Delaware River, Kent County, Delaware, and two Maryland counties.

What is the population of New Castle County?
570,719 at the 2020 census, with an estimate near 588,026 by 2025.

How big is New Castle County?
494 square miles (1,280 km2) in total, of which 426 square miles are land.

What is the county seat of New Castle County?
Wilmington, Delaware’s largest city, is the county seat.

How many towns and cities are in New Castle County?
Thirteen incorporated places — the cities of Wilmington, Newark, New Castle and Delaware City; the towns of Middletown, Elsmere, Newport, Odessa, Townsend and Bellefonte; and the villages of Arden, Ardentown and Ardencroft — plus 13 unincorporated census-designated places.

What ZIP codes does New Castle County use?
Wilmington alone spans more than a dozen ZIPs from 19801 through 19899; other towns run from 19702 (Newark) to 19734 (Townsend), with Arden, Ardentown and Ardencroft sharing 19810.

What is New Castle County known for?
Wilmington’s role as a national credit-card banking center since 1981, the DuPont company’s gunpowder-mill origins on the Brandywine, and the Battle of Cooch’s Bridge near Newark, Delaware’s only Revolutionary War battle.

More counties in this state: Towns and villages in Delaware.