When was Adams County founded?

Adams County was founded in 1797, formed from Hamilton County and Washington County, and named after John Adams.

What is the county seat of Adams County?

The county seat of Adams County is West Union.

Is there an online parcel map for Adams County?

Yes. Ohio Geographically Referenced Information Program (OGRIP, Ohio DAS) statewide compilation of county auditor parcels publishes a parcel map of 21,554 parcels, rated fallback here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Adams County's boundary or name changed?

Adams County was created in 1797 from Hamilton County and Washington County. Since then the Atlas of Historical County Boundaries records 7 later changes, chiefly involving Brown County, Hamilton County and Highland County.

Is my lot in a flood zone?

We do not have flood maps for Adams County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

County · code 39001

Adams CountyOhio

Adams County is a county in Ohio with its seat in West Union. It was created on July 10, 1797, by the Northwest Territory from Hamilton and Washington Counties.

Founded1797
County seatWest Union
Named forJohn Adams
Land area584 sq mi + 2.4 sq mi water
Population27,477 2020 Census
Parcels mapped21,554 checked 14 October 2026

Open the free map Click any parcel in Adams County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated 20 October 2026

Census outline · seat marked

History

Formed in 1797 from Hamilton County and Washington County

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

Adams County was formed in 1797 from Hamilton and Washington Counties and named after John Adams. The county became part of the state of Ohio in 1803, and it was reduced through the creation of several neighboring counties: Ross, Scioto, Highland, Pike, and Brown.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

1797
Adams County created Adams created by the Northwest Territory from Hamilton and Washington.
from Hamilton from Washington
10 July 1797 · Terr. Papers U.S., 2:612-613; Chase, 3:ch. 333/p. 2096
1798
Lost territory Adams lost to creation of Ross.
to Ross
20 August 1798 · Terr. Papers U.S., 3:510; Chase, 3:ch. 336/p. 2097
1798
Gained territory Adams gained from Hamilton.
from Hamilton
1 September 1798 · Terr. Papers U.S., 3:510-511; Chase, 3:ch. 337/p. 2097
1803
Became part of Ohio Adams became a county in the state of Ohio. 1 March 1803 · U.S. Stat., vol. 2, ch. 40 [1802], secs. 1-3/pp. 173-174; Van Zandt, 112
1803
Lost territory Adams lost to creation of Scioto.
to Scioto
1 May 1803 · Ohio Laws 1803, 1st assy., ch. 3/p. 8; Chase, 3:ch. 344/p. 2099

Show all 9 changes (4 more)

1797
Adams County created Adams created by the Northwest Territory from Hamilton and Washington.
from Hamilton from Washington
10 July 1797 · Terr. Papers U.S., 2:612-613; Chase, 3:ch. 333/p. 2096
1798
Lost territory Adams lost to creation of Ross.
to Ross
20 August 1798 · Terr. Papers U.S., 3:510; Chase, 3:ch. 336/p. 2097
1798
Gained territory Adams gained from Hamilton.
from Hamilton
1 September 1798 · Terr. Papers U.S., 3:510-511; Chase, 3:ch. 337/p. 2097
1803
Became part of Ohio Adams became a county in the state of Ohio. 1 March 1803 · U.S. Stat., vol. 2, ch. 40 [1802], secs. 1-3/pp. 173-174; Van Zandt, 112
1803
Lost territory Adams lost to creation of Scioto.
to Scioto
1 May 1803 · Ohio Laws 1803, 1st assy., ch. 3/p. 8; Chase, 3:ch. 344/p. 2099
1805
Lost territory Adams lost to creation of Highland.
to Highland
1 May 1805 · Ohio Laws 1804, 3d assy., ch. 60, sec. 1/p. 256; Chase, 3: ch. 350/p. 2102
1815
Lost territory Adams lost small area to creation of Pike.
to Pike
1 February 1815 · Ohio Laws 1814, 13th assy., ch. 16, secs. 1, 6/pp. 52, 55; Chase 3:ch. 399/pp. 2118-2119
1818
Lost territory Adams lost to creation of Brown.
to Brown
1 March 1818 · Ohio Laws 1817, 16th assy., ch. 12, secs. 1, 6/pp. 29, 31; Chase, 3:ch. 412/pp. 2124-2125
1819
Boundary clarified Boundary between Adams and Brown was clarified (no change).
with Brownno change
5 February 1819 · Ohio Laws 1818, 17th assy., ch. 57/p. 130; Chase 3: ch. 425/p. 2132

Land and parcels

What the maps cover in Adams

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

Parcels Fallback

Lot lines and tax-map numbers for 21,554 parcels from Ohio Geographically Referenced Information Program (OGRIP, Ohio DAS) statewide compilation of county auditor parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey. This copy is a fallback, not the county's own: use it as a guide and check the official record.
edited 23 September 2026 · checked 14 October 2026
Address points Official

One point per address, 16,012 in all from Ohio Geographically Referenced Information Program (OGRIP), Ohio DAS/OIT (state GIS office).
edited 24 June 2025 · checked 13 October 2026
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

Adams by the Census

Population

27,477 2020 Census count

Housing units

12,692 2020 Census count

Land area

584 square miles

Water area

2.4 square miles

People per sq mi

47 population ÷ land area

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

See your own lot on these maps

Open Adams 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.

Open the free map no sign-in Pro early access

Questions

Common questions about Adams County

When was Adams County founded?: Adams County was founded in 1797, formed from Hamilton County and Washington County, and named after John Adams.
What is the county seat of Adams County?: The county seat of Adams County is West Union.
Is there an online parcel map for Adams County?: Yes. Ohio Geographically Referenced Information Program (OGRIP, Ohio DAS) statewide compilation of county auditor parcels publishes a parcel map of 21,554 parcels, rated fallback here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Adams County's boundary or name changed?: Adams County was created in 1797 from Hamilton County and Washington County. Since then the Atlas of Historical County Boundaries records 7 later changes, chiefly involving Brown County, Hamilton County and Highland County.
Is my lot in a flood zone?: We do not have flood maps for Adams County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

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