When was Madison County founded?

Madison County was founded in 1810, formed from Franklin County, and named after James Madison.

What is the county seat of Madison County?

The county seat of Madison County is London.

Is there an online parcel map for Madison County?

Yes. Madison County publishes a parcel map of 24,915 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Madison County's boundary or name changed?

Madison County was created in 1810 from Franklin County. Since then the Atlas of Historical County Boundaries records 5 later changes, chiefly involving Franklin County, Clark County and Champaign County.

Who issues building permits in Madison County?

The county's page on building permits: Building permits. Inside a city or town, ask that city first.

Who issues septic and well permits in Madison County?

The county's page on septic systems and wells: Who To Contact.

Is my lot in a flood zone?

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

County · code 39097

Madison CountyOhio

Madison County is a county in Ohio with its seat in London. It was created in 1810 from Franklin County and named after James Madison.

Founded1810
County seatLondon
Named forJames Madison
Land area466 sq mi + 0.8 sq mi water
Population43,824 2020 Census
Parcels mapped24,915 checked 15 October 2026

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

Updated 19 October 2026

Census outline · seat marked

History

Formed in 1810 from Franklin County

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

Madison County was created from Franklin County in 1810. In 1818, Madison County gained territory from Champaign County and lost territory to the creation of Clark County. In 1820, the county gained from Franklin County and lost territory to the creation of Union County. Madison County exchanged territory with Clark County in 1827 and with Franklin County in 1845.

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

1810
Madison County created Madison created from Franklin.
from Franklin
1 March 1810 · Ohio Laws 1809, 8th assy., ch. 67/p. 248; Chase, 3:ch. 385/p. 2114
1818
Gained territory Madison gained from Champaign, lost to creation of Clark.
from Champaign from Clark
1 March 1818 · Ohio Laws 1817, 16th assy., chs. 14, 33/pp. 33, 36, 75; Chase, 3:chs. 413, 418/pp. 2125-2126, 2129
1820
Gained territory Madison gained from Franklin, lost to creation of Union.
from Franklin from Union
1 April 1820 · Ohio Laws 1819, 18th assy., loc., ch. 16, secs. 1, 8-9/pp. 56, 58; Chase, 3:ch. 428/p. 2133
1827
Exchanged territory Madison exchanged with Clark.
with Clark
22 January 1827 · Ohio Laws 1826, 25th assy., gen., p. 24; Chase, 3:ch. 455/pp. 2141-2142
1845
Exchanged territory Madison exchanged with Franklin.
with Franklin
4 March 1845 · Ohio Laws 1844, 43d assy., loc., p. 196

Show all 8 changes (3 more, mostly small adjustments)

1810
Madison County created Madison created from Franklin.
from Franklin
1 March 1810 · Ohio Laws 1809, 8th assy., ch. 67/p. 248; Chase, 3:ch. 385/p. 2114
1818
Gained territory Madison gained from Champaign, lost to creation of Clark.
from Champaign from Clark
1 March 1818 · Ohio Laws 1817, 16th assy., chs. 14, 33/pp. 33, 36, 75; Chase, 3:chs. 413, 418/pp. 2125-2126, 2129
1820
Gained territory Madison gained from Franklin, lost to creation of Union.
from Franklin from Union
1 April 1820 · Ohio Laws 1819, 18th assy., loc., ch. 16, secs. 1, 8-9/pp. 56, 58; Chase, 3:ch. 428/p. 2133
1821
Boundary clarified Boundary between Madison and Union was clarified (no change).
with Unionno change
29 January 1821 · Ohio Laws 1820, 19th assy., ch. 44/p. 73; Chase, 3:ch. 431/p. 2135
1827
Exchanged territory Madison exchanged with Clark.
with Clark
22 January 1827 · Ohio Laws 1826, 25th assy., gen., p. 24; Chase, 3:ch. 455/pp. 2141-2142
1827
Boundary clarified Boundary between Madison and Union was clarified (no change).
with Unionno change
29 January 1827 · Ohio Laws 1826, 25th assy., gen., p. 99; Chase, 3:ch. 457/pp. 2142-2143
1845
Exchanged territory Madison exchanged with Franklin.
with Franklin
4 March 1845 · Ohio Laws 1844, 43d assy., loc., p. 196
1857
Changed Legislature authorized Franklin to gain from Madison dependent on local referendum.
Franklin
3 April 1857 · Ohio Laws 1857, 52d assy., 2d sess., p. 260

Land and parcels

What the maps cover in Madison

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

Parcels Good enough

Lot lines and tax-map numbers for 24,915 parcels from Madison County. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 27 March 2025 · checked 15 October 2026
Address points Official

One point per address, 20,204 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

Madison by the Census

Population

43,824 2020 Census count

Housing units

16,216 2020 Census count

Land area

466 square miles

Water area

0.8 square miles

People per sq mi

94 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

Who to ask before you build, dig or sell

Official county pages only. We link to them; we do not copy them, because they change.

Inside a city or town, permits usually come from that city rather than the county.

Permits

Health department: septic and well
Who To Contact
from co.madison.oh.us · checked 13 October 2026
Building permitsfrom co.madison.oh.us
Building Permitfrom co.madison.oh.us
Septic and Sewage Systemsfrom co.madison.oh.us

Zoning and code

Planning and zoningfrom co.madison.oh.us · checked 13 October 2026
Zoning Resolution as adopted July 28 2026from co.madison.oh.us
Planning & Zoningfrom co.madison.oh.us

GIS and maps

County GIS and mapsfrom co.madison.oh.us · checked 13 October 2026

County government

County government
The official website of Madison County.
co.madison.oh.us

See your own lot on these maps

Open Madison 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 Madison County

When was Madison County founded?: Madison County was founded in 1810, formed from Franklin County, and named after James Madison.
What is the county seat of Madison County?: The county seat of Madison County is London.
Is there an online parcel map for Madison County?: Yes. Madison County publishes a parcel map of 24,915 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Madison County's boundary or name changed?: Madison County was created in 1810 from Franklin County. Since then the Atlas of Historical County Boundaries records 5 later changes, chiefly involving Franklin County, Clark County and Champaign County.
Who issues building permits in Madison County?: The county's page on building permits: Building permits. Inside a city or town, ask that city first.
Who issues septic and well permits in Madison County?: The county's page on septic systems and wells: Who To Contact.
Is my lot in a flood zone?: We do not have flood maps for Madison 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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