County · code 10003
New Castle CountyDelaware
New Castle County is a county in Delaware, with Wilmington as its county seat. The county was created in 1673 by the Dutch as New Amstel.
- Founded1664
- County seatWilmington
- Named forNew Castle, Delaware
- Land area426 sq mi + 68 sq mi water
- Population570,719 2020 Census
- Parcels mapped203,818 checked 15 October 2026
Where it is
New Castle on the map of Delaware
Delaware has 3 counties and county equivalents, each with its own records office. Shapes with a page are links.
History
Founded in 1664
An old deed may name a county that no longer exists, or a boundary that has since moved.
The Dutch created New Castle County in 1673 as New Amstel, one of three original counties in Delaware. New Amstel was renamed New Castle by November 1674 after the Dutch returned the area to the Duke of York following the Treaty of Westminster. The county was transferred from New York to Pennsylvania with William Penn in 1682, then separated from Pennsylvania when Delaware became a distinct colony in 1704.
- 1673New Castle County created After completing their re-conquest of New York in August 1673, the Dutch created New Amstel (now New Castle) as one of three countylike courts that became original counties in Delaware; no inland limits specified. · Docs. of N.Y., 12:507-508; George, Nead, and McCamant, 453-454; Reed, 22
- 1674Renamed By 11 November 1674, New Amstel was renamed New Castle.formerly By 11 November 1674, New Amstel Was· Docs. of N.Y., 12:515
- 1678Gained territory New Castle gained from Upland (extinct).from Upland· Armstrong, 119, 198
- 1685Eliminated King James Ii approved decision of the Committee for Trade and Plantations (7 November 1685) settling the rival claims of Maryland and Pennsylvania to Pennsylvania's Lower Counties, now Delaware. Worcester (Md., original, extinct) eliminated, ending its overlap with New Castle (Delaware)into Iiinto Worcester· Lunt, 47; Report on the Resurvey, 145; Van Zandt, 81
- 1704Independent city separated By 29 November 1704, New Castle was separated from Pennsylvania when Delaware became a distinct colony. · Penn, 4:309; Rodney, 239
Show all 15 changes
- 1673New Castle County created After completing their re-conquest of New York in August 1673, the Dutch created New Amstel (now New Castle) as one of three countylike courts that became original counties in Delaware; no inland limits specified. · Docs. of N.Y., 12:507-508; George, Nead, and McCamant, 453-454; Reed, 22
- 1674Changed In the Autumn of 1674, the Dutch returned New York and the Delaware River settlements, including New Amstel (now New Castle) to the Duke of York in accordance with the Treaty of Westminster (9 February 1673/1674). By 6 November 1674 New Amstel was made dependent on New York, although Maryland also claimed the area. · Docs. of N.Y., 12:515; George, Nead, and McCamant, 454; Parry, 13:136
- 1674Renamed By 11 November 1674, New Amstel was renamed New Castle.formerly By 11 November 1674, New Amstel Was· Docs. of N.Y., 12:515
- 1676Changed The Duke of York's laws were extended from New York to the Delaware region; New Castle was formally placed under the Duke of York's laws. · Docs. of N.Y., 12:561-563, Reed, 13
- 1678Gained territory New Castle gained from Upland (extinct).from Upland· Armstrong, 119, 198
- 1680Lost territory New Castle lost to creation of St. Jones (now Kent).to St. Jonesto Kent· Docs. of N.Y., 12:654, 664, 666-667; Reed, 12
- 1682Gained territory New Castle was transferred with the rest of the western Delaware Bay region from the Duke of York to William Penn. New Castle Implicitly gained the southern remnant of Upland (extinct) south of the 12-mile circular boundary around New Castle established 4 March 1680/1681 as the northern limit of the Delaware region.from Upland· Pa. Archives, 2d ser., 5:739-744
- 1682Changed William Penn annexed the Delaware River region to Pennsylvania. New Castle became part of the area known as the Territories or Lower Counties of Pennsylvania. Maryland did not abandon its claim to the Delaware region but had no control there. · Swindler, 2:191-192
- 1685Eliminated King James Ii approved decision of the Committee for Trade and Plantations (7 November 1685) settling the rival claims of Maryland and Pennsylvania to Pennsylvania's Lower Counties, now Delaware. Worcester (Md., original, extinct) eliminated, ending its overlap with New Castle (Delaware)into Iiinto Worcester· Lunt, 47; Report on the Resurvey, 145; Van Zandt, 81
- 1687
- 1704Independent city separated By 29 November 1704, New Castle was separated from Pennsylvania when Delaware became a distinct colony. · Penn, 4:309; Rodney, 239
- 1775Changed New Castle boundary was completed westward to the Maryland line. · Del., Laws of the State, vol. 1, ch. 229, sec. 4/pp. 569-570
- 1776Changed The three Lower Counties, including New Castle, became an independent state. The name Delaware was formally adopted on 20 September 1776. · Declaration of Independence; Swindler, 2:197
- 1841Lost territory New Castle lost to Kent. · Del. Laws 1841, ch. 347/pp. 401-402; Scharf, 2:1030
- 1921Exchanged territory New Castle exchanged narrow strips of territory with Chester (Pennsylvania) when the U.S. Congress ratified the agreement between Delaware and Pennsylvania on the demarcation of their common boundary. New Castle lost a small sliver of territory along the circular line (known as the Horn) and gained a small triangular area by the northeast corner of Maryland (known as the Wedge).with Chester (Pa.)with U.s.· Lunt, 59, 61; Van Zandt, 83
Land and parcels
What the maps cover in New Castle
Who publishes each layer, how good it is, and when we last checked.
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Parcels Good enough
Lot lines and tax-map numbers for 203,818 parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 15 October 2026 -
Address points Missing
No public address points layer found for New Castle County yet.
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Buildings Reference
Roof outlines traced from aerial imagery from FEMA Response Geospatial Office with Oak Ridge National Laboratory (ORNL). Good for seeing what is on a lot; not accurate enough to set a fence from.
checked 18 October 2026
- Official
- from the office that keeps the record
- Good enough
- a reliable statewide or national copy
- Fallback
- a guide only; check the official record
- Missing
- nothing public found yet
People and land
New Castle by the Census
Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.
Rules and offices
New Castle County's official site
We have found the county's site but not its offices yet; start there.
County government
- County government
The official website of New Castle County.
See your own lot on these maps
Open New Castle County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.
Questions
Common questions about New Castle County
- When was New Castle County founded?
- New Castle County was founded in 1664, and named after New Castle, Delaware.
- What is the county seat of New Castle County?
- The county seat of New Castle County is Wilmington.
- Is there an online parcel map for New Castle County?
- Yes. A public source publishes a parcel map of 203,818 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
- Has New Castle County's boundary or name changed?
- New Castle County was created in 1673. Since then the Atlas of Historical County Boundaries records 14 later changes, chiefly involving Kent County, Upland County and Chester (Pa.) County. It was formerly called By 11 November 1674, New Amstel Was.
- Is my lot in a flood zone?
- We do not have flood maps for New Castle County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.
Nearby