When was Montgomery County founded?

Montgomery County was founded in 1803, formed from Hamilton County, and named after Richard Montgomery.

What is the county seat of Montgomery County?

The county seat of Montgomery County is Dayton.

Is there an online parcel map for Montgomery County?

Yes. Ohio Geographically Referenced Information Program (OGRIP, Ohio DAS) statewide compilation of county auditor parcels publishes a parcel map of 273,090 parcels, rated fallback here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Montgomery County's boundary or name changed?

Montgomery County was created in 1803 from Hamilton County. Since then the Atlas of Historical County Boundaries records 3 later changes, chiefly involving Miami County, Darke County and Preble County.

Is my lot in a flood zone?

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

County · code 39113

Montgomery CountyOhio

Montgomery County is a county in Ohio, with its seat in Dayton, formed on May 1, 1803.

Founded1803
County seatDayton
Named forRichard Montgomery
Land area461 sq mi + 2.9 sq mi water
Population537,309 2020 Census
Parcels mapped273,090 checked 14 October 2026

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

Updated 19 October 2026

Census outline · seat marked

History

Formed in 1803 from Hamilton County

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

Montgomery County was created from Hamilton County on May 1, 1803, and named after Richard Montgomery. The county lost territory over the following decade: Miami County was created from it in 1807, and Preble County in 1808.

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

1803
Montgomery County created Montgomery created from Hamilton and Non-County Area 1.
from Hamilton
1 May 1803 · Ohio Laws 1803, 1st assy., ch. 4, secs. 1-4, 8/pp. 9-12; Chase, 3:ch. 345/pp. 2099-2100
1807
Lost territory Montgomery lost to creation of Miami.
to Miami
1 April 1807 · Ohio Laws 1806, 5th assy., ch. 32, secs. 1-2, 5/pp. 94-96; Chase, 3:ch. 357/p. 2104
1808
Lost territory Montgomery lost to creation of Preble.
to Preble
1 March 1808 · Ohio Laws 1807, 6th assy., ch. 51, secs. 1-2, 5/pp. 164-166; Chase, 3:ch. 369/p. 2109
1812
Changed That part of Montgomery lying north of the Indian Boundary reverted to Non-County Area 6 attached to Darke and Non-County Area 7 attached to Miami. Attachments were for administrative and judicial purposes.
Darke Miami
7 January 1812 · Ohio Laws 1811, 10th assy., ch. 13/p. 22; Chase, 3:ch. 390/p. 2115

Land and parcels

What the maps cover in Montgomery

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

Parcels Fallback

Lot lines and tax-map numbers for 273,090 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, 255,268 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

Montgomery by the Census

Population

537,309 2020 Census count

Housing units

251,523 2020 Census count

Land area

461 square miles

Water area

2.9 square miles

People per sq mi

1,165 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

Montgomery 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 Montgomery County.
mcohio.org

See your own lot on these maps

Open Montgomery 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 Montgomery County

When was Montgomery County founded?: Montgomery County was founded in 1803, formed from Hamilton County, and named after Richard Montgomery.
What is the county seat of Montgomery County?: The county seat of Montgomery County is Dayton.
Is there an online parcel map for Montgomery County?: Yes. Ohio Geographically Referenced Information Program (OGRIP, Ohio DAS) statewide compilation of county auditor parcels publishes a parcel map of 273,090 parcels, rated fallback here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Montgomery County's boundary or name changed?: Montgomery County was created in 1803 from Hamilton County. Since then the Atlas of Historical County Boundaries records 3 later changes, chiefly involving Miami County, Darke County and Preble County.
Is my lot in a flood zone?: We do not have flood maps for Montgomery 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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