When was Petroleum County founded?

Petroleum County was founded in 1925, formed from Fergus County, and named after petroleum.

What is the county seat of Petroleum County?

The county seat of Petroleum County is Winnett.

Is there an online parcel map for Petroleum County?

Yes. Montana State Library (Montana Cadastral Framework; data from MT Dept of Revenue ORION and five counties) publishes a parcel map of 4,523 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Petroleum County's boundary or name changed?

Petroleum County was created in 1925 from Fergus County. The Atlas of Historical County Boundaries records no boundary change since.

Is my lot in a flood zone?

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

County · code 30069

Petroleum CountyMontana

Petroleum County is a county in Montana with its seat in Winnett, formed in 1925.

Founded1925
County seatWinnett
Named forpetroleum
Land area1,656 sq mi + 19 sq mi water
Population496 2020 Census
Parcels mapped4,523 checked 16 October 2026

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

Updated 19 October 2026

Census outline · seat marked

History

Formed in 1925 from Fergus County

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

Petroleum County was created by petition and election from Fergus County on February 22, 1925.

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

1925
Petroleum County created Petroleum created by petition and election from Fergus.
from Fergus
22 February 1925 · Mont. Laws 1925, 19th leg., pp. 505-508; "State ex rel. Foot v. Burr et al.," in Mont. Rpts., 73: 586-590

Land and parcels

What the maps cover in Petroleum

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

Parcels Good enough

Lot lines and tax-map numbers for 4,523 parcels from Montana State Library (Montana Cadastral Framework; data from MT Dept of Revenue ORION and five counties). Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
edited 13 October 2026 · checked 16 October 2026
Address points Official

One point per address, 478 in all from Montana State Library.
edited 13 October 2026 · checked 14 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

Petroleum by the Census

Population

496 2020 Census count

Housing units

333 2020 Census count

Land area

1,656 square miles

Water area

19 square miles

People per sq mi

<1 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

Petroleum 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 Petroleum County.
petroleumcountymt.com

See your own lot on these maps

Open Petroleum 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 Petroleum County

When was Petroleum County founded?: Petroleum County was founded in 1925, formed from Fergus County, and named after petroleum.
What is the county seat of Petroleum County?: The county seat of Petroleum County is Winnett.
Is there an online parcel map for Petroleum County?: Yes. Montana State Library (Montana Cadastral Framework; data from MT Dept of Revenue ORION and five counties) publishes a parcel map of 4,523 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Petroleum County's boundary or name changed?: Petroleum County was created in 1925 from Fergus County. The Atlas of Historical County Boundaries records no boundary change since.
Is my lot in a flood zone?: We do not have flood maps for Petroleum County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby