When was Beaverhead County founded?

Beaverhead County was founded in 1864, and named after Beaverhead Rock, Montana.

What is the county seat of Beaverhead County?

The county seat of Beaverhead County is Dillon.

Is there an online parcel map for Beaverhead County?

Yes. A public source publishes a parcel map of 16,125 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Beaverhead County's boundary or name changed?

Beaverhead County was created in 1864. Since then the Atlas of Historical County Boundaries records 7 later changes, chiefly involving Madison County, Deer Lodge County and Jefferson County.

Is my lot in a flood zone?

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

County · code 30001

Beaverhead CountyMontana

Beaverhead County is a county in Montana with its seat in Dillon, formed in 1864. The county takes its name from Beaverhead Rock.

Founded1864
County seatDillon
Named forBeaverhead Rock, Montana
Land area5,543 sq mi + 30 sq mi water
Population9,371 2020 Census
Parcels mapped16,125 checked 14 October 2026

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

Updated 20 October 2026

Census outline · seat marked

History

Founded in 1864

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

Beaverhead County was created by Idaho Territory on January 16, 1864. It became a Montana Territory county on May 26, 1864, and later became a county in the state of Montana on November 8, 1889. The county experienced multiple boundary adjustments over its early years, gaining and losing territory to neighboring counties including Jefferson, Madison, and Deer Lodge.

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

1864
Beaverhead County created Beaverhead created by Idaho Territory from non-county area. 16 January 1864 · Idaho Terr. Laws 1863, 1st sess., sec. 3/p. 675
1864
Became part of Montana Beaverhead became a county in Montana Territory. On 22 September 1864, Montana Territorial Governor, Sidney Edgerton, recognized the counties created by Idaho Territory in an election proclamation. 26 May 1864 · U.S. Stat., vol. 13, ch. 95 [1864], sec. 1/pp. 85-92; Sanders, Helen F., 1:329; Van Zandt, 145
1865
Beaverhead County created Beaverhead re-created by Montana Territory; Beaverhead gained from Jefferson and Madison, lost to Deer Lodge.
from Jefferson from Madison from Deer Lodge
2 February 1865 · Mont. Terr. Laws 1864, 1st leg., sec. 3/p. 529
1867
Lost territory Beaverhead lost to Madison.
to Madison
10 December 1867 · Mont. Terr. Laws 1867, 4th leg., sec. 2/pp. 102-103
1889
Became part of Montana Beaverhead became a county in the state of Montana. 8 November 1889 · U.S. Stat., vol. 26, pp. 1551-1552 and vol. 25, ch. 180 [1889]/pp. 676-684; Swindler, 6:82-83

Show all 10 changes (5 more)

1864
Beaverhead County created Beaverhead created by Idaho Territory from non-county area. 16 January 1864 · Idaho Terr. Laws 1863, 1st sess., sec. 3/p. 675
1864
Became part of Montana Beaverhead became a county in Montana Territory. On 22 September 1864, Montana Territorial Governor, Sidney Edgerton, recognized the counties created by Idaho Territory in an election proclamation. 26 May 1864 · U.S. Stat., vol. 13, ch. 95 [1864], sec. 1/pp. 85-92; Sanders, Helen F., 1:329; Van Zandt, 145
1865
Beaverhead County created Beaverhead re-created by Montana Territory; Beaverhead gained from Jefferson and Madison, lost to Deer Lodge.
from Jefferson from Madison from Deer Lodge
2 February 1865 · Mont. Terr. Laws 1864, 1st leg., sec. 3/p. 529
1867
Lost territory Beaverhead lost to Madison.
to Madison
10 December 1867 · Mont. Terr. Laws 1867, 4th leg., sec. 2/pp. 102-103
1869
Lost territory Beaverhead lost to Madison.
to Madison
12 January 1869 · Mont. Terr. Laws 1868, 5th leg., p. 105
1872
Exchanged territory Beaverhead exchanged with Deer Lodge.
with Deer Lodge
12 January 1872 · Mont. Terr. Laws 1871, 7th leg., ch. 20, secs. 2-3/pp. 429-430
1874
Changed Beaverhead authorized to gain part of the remnant of Dakota Territory which was transferred to Montana Territory on 17 February 1873. This act appears to have been based on faulty maps, since the area was actually surrounded by Gallatin (no change).
Gallatin
7 February 1874 · Mont. Terr. Laws 1874, 8th leg., p. 68; Van Zandt, 136, 145, 150; De Lacy, Map of the Territory of Montana
1887
Boundary clarified Beaverhead boundaries redefined (no change).
no change
1 March 1887 · Mont. Terr. Laws 1887, 15th leg., sec. 732/p. 834
1889
Became part of Montana Beaverhead became a county in the state of Montana. 8 November 1889 · U.S. Stat., vol. 26, pp. 1551-1552 and vol. 25, ch. 180 [1889]/pp. 676-684; Swindler, 6:82-83
1911
Gained territory Beaverhead gained from Madison.
from Madison
2 March 1911 · Mont. Laws 1911, 12th leg., ch. 73/pp. 137-141

Land and parcels

What the maps cover in Beaverhead

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

Parcels Good enough

Lot lines and tax-map numbers for 16,125 parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 14 October 2026
Address points Official

One point per address, 6,272 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

Beaverhead by the Census

Population

9,371 2020 Census count

Housing units

4,918 2020 Census count

Land area

5,543 square miles

Water area

30 square miles

People per sq mi

2 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

Beaverhead 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 Beaverhead County.
beaverheadcounty.org

See your own lot on these maps

Open Beaverhead 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 Beaverhead County

When was Beaverhead County founded?: Beaverhead County was founded in 1864, and named after Beaverhead Rock, Montana.
What is the county seat of Beaverhead County?: The county seat of Beaverhead County is Dillon.
Is there an online parcel map for Beaverhead County?: Yes. A public source publishes a parcel map of 16,125 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Beaverhead County's boundary or name changed?: Beaverhead County was created in 1864. Since then the Atlas of Historical County Boundaries records 7 later changes, chiefly involving Madison County, Deer Lodge County and Jefferson County.
Is my lot in a flood zone?: We do not have flood maps for Beaverhead County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby