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County · code 17111

McHenry CountyIllinois

McHenry County is a county in Illinois with its seat in Woodstock, founded in 1836. It was named after William McHenry.

  • Founded1836
  • County seatWoodstock
  • Named forWilliam McHenry
  • Land area603 sq mi + 7.7 sq mi water
  • Population310,229 2020 Census
  • Parcels mapped150,153 checked 16 October 2026
Open the free map Click any parcel in McHenry County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated

Walworth, WIBooneKaneLake Woodstock Census outline · seat marked

Where it is

McHenry on the map of Illinois

Illinois has 102 counties and county equivalents, each with its own records office. Shapes with a page are links.

Adams CountyAlexander CountyBond CountyBoone CountyBrown CountyBureau CountyCalhoun CountyCarroll CountyCass CountyChampaign CountyChristian CountyClark CountyClay CountyClinton CountyColes CountyCook CountyCrawford CountyCumberland CountyDeKalb CountyDe Witt CountyDouglas CountyDuPage CountyEdgar CountyEdwards CountyEffingham CountyFayette CountyFord CountyFranklin CountyFulton CountyGallatin CountyGreene CountyGrundy CountyHamilton CountyHancock CountyHardin CountyHenderson CountyHenry CountyIroquois CountyJackson CountyJasper CountyJefferson CountyJersey CountyJo Daviess CountyJohnson CountyKane CountyKankakee CountyKendall CountyKnox CountyLake CountyLaSalle CountyLawrence CountyLee CountyLivingston CountyLogan CountyMcDonough CountyMcLean CountyMacon CountyMacoupin CountyMadison CountyMarion CountyMarshall CountyMason CountyMassac CountyMenard CountyMercer CountyMonroe CountyMontgomery CountyMorgan CountyMoultrie CountyOgle CountyPeoria CountyPerry CountyPiatt CountyPike CountyPope CountyPulaski CountyPutnam CountyRandolph CountyRichland CountyRock Island CountySt. Clair CountySaline CountySangamon CountySchuyler CountyScott CountyShelby CountyStark CountyStephenson CountyTazewell CountyUnion CountyVermilion CountyWabash CountyWarren CountyWashington CountyWayne CountyWhite CountyWhiteside CountyWill CountyWilliamson CountyWinnebago CountyWoodford CountyMcHenry County McHenry
Counties of Illinois · McHenry highlighted

History

Founded in 1836

An old deed may name a county that no longer exists, or a boundary that has since moved.

McHenry County was created on January 16, 1836, from Cook County and Non-County Area 8 (attached to La Salle County), but was not fully organized until it was detached from Cook on March 1, 1837. On March 1, 1839, McHenry County lost territory to the creation of Lake County.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries.

  1. 1836
    McHenry County created McHenry created from Cook and Non-County Area 8 attached to La Salle; McHenry not fully organized, attached to Cook until "organized".
    from Cookfrom La Salle
    · Ill. Laws 1835-1836, pp. 273-278
  2. 1837
    Changed McHenry fully organized, detached from Cook; McHenry's boundaries were extended to the Illinois state limits in Lake Michigan.
    Cook
    · Ill. Laws 1836-1837, pp. 89-90
  3. 1839
    Lost territory McHenry lost to creation of Lake.
    to Lake
    · Ill. Laws 1838-1839, pp. 216-217
  4. 1839
    Changed Legislature authorized Boone to gain townships 43 to 46, range 5 east, fromf McHenry, dependent on local referendum that failed (no change).
    Boone
    · Ill. Laws 1838-1839, p. 242
  5. 1843
    Boundary clarified McHenry boundaries were redefined (no change).
    no change
    · Ill. Laws 1842-1843, p. 91

Land and parcels

What the maps cover in McHenry

Who publishes each layer, how good it is, and when we last checked.

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

McHenry by the Census

Population
310,229 2020 Census count
Housing units
119,708 2020 Census count
Land area
603 square miles
Water area
7.7 square miles
People per sq mi
514 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

Rules and offices

McHenry County's official site

We have found the county's site but not its offices yet; start there.

County government

See your own lot on these maps

Open McHenry 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.

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Questions

Common questions about McHenry County

When was McHenry County founded?
McHenry County was founded in 1836, and named after William McHenry.
What is the county seat of McHenry County?
The county seat of McHenry County is Woodstock.
Is there an online parcel map for McHenry County?
Yes. McHenry County publishes a parcel map of 150,153 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has McHenry County's boundary or name changed?
McHenry County was created in 1836. Since then the Atlas of Historical County Boundaries records 2 later changes, chiefly involving Cook County and Lake County.
Is my lot in a flood zone?
We do not have flood maps for McHenry County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby

Counties next door