What is the county seat of Lewis and Clark County?

The county seat of Lewis and Clark County is Helena.

Is there an online parcel map for Lewis and Clark County?

Yes. A public source publishes a parcel map of 40,293 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.

Has Lewis and Clark County's boundary or name changed?

Lewis and Clark County was created in 1865 from Choteau County, Chouteau County and Jefferson County. Since then the Atlas of Historical County Boundaries records 12 later changes, chiefly involving Lewis and Clarke County, Cascade County and Choteau County. It was formerly called Edgerton.

Who issues building permits in Lewis and Clark County?

The county's page on building permits: Catering Permit - Lewis & Clark County. Inside a city or town, ask that city first.

Who issues septic and well permits in Lewis and Clark County?

The county's page on septic systems and wells: Contact Public Health.

Is my lot in a flood zone?

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

County · code 30049

Lewis and Clark CountyMontana

Lewis and Clark County is a county in Montana with its seat in Helena, formed in 1865.

Founded1865
County seatHelena
Named forWilliam Clark and Meriwether Lewis
Land area3,458 sq mi + 39 sq mi water
Population70,973 2020 Census
Parcels mapped40,293 checked 15 October 2026

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

Updated 20 October 2026

Census outline · seat marked

History

Formed in 1865 from Choteau County, Chouteau County and Jefferson County

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

Originally created as Edgerton County from Choteau and Jefferson counties in the Montana Territory, it was renamed Lewis and Clark in 1868 and named after explorers Meriwether Lewis and William Clark. The county became part of the state of Montana in 1889 and gained and lost territory through multiple boundary adjustments with neighboring counties over the following decades.

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

1865
Lewis and Clark County created Edgerton (now Lewis and Clark) created by Montana Territory from Choteau (now Chouteau) and Jefferson.
from Choteau from Chouteaufrom Jefferson
2 February 1865 · Mont. Terr. Laws 1864, 1st leg., sec. 6/p. 530
1867
Gained territory Edgerton (now Lewis and Clark) gained from Deer Lodge, exchanged with Jefferson.
from Deer Lodge from Jefferson
21 November 1867 · Mont. Terr. Laws 1867, 4th leg., p. 101
1868
Renamed Edgerton renamed Lewis and Clark; legislation used the spelling "Lewis and Clarke". Act passed 20 December 1867; took effect 1 March 1868.
formerly Edgerton
1 March 1868 · Mont. Terr. Laws 1867, 4th leg., p. 130
1889
Became part of Montana Lewis and Clark 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
1905
Lewis and Clark County created Spelling of Lewis and Clark officially established as "Clark," not "Clarke."
from Clarkfrom Clarke
10 February 1905 · Mont. Laws 1905, 9th leg., ch. 13/p. 28

Show all 15 changes (10 more, mostly small adjustments)

1865
Lewis and Clark County created Edgerton (now Lewis and Clark) created by Montana Territory from Choteau (now Chouteau) and Jefferson.
from Choteau from Chouteaufrom Jefferson
2 February 1865 · Mont. Terr. Laws 1864, 1st leg., sec. 6/p. 530
1867
Gained territory Edgerton (now Lewis and Clark) gained from Deer Lodge, exchanged with Jefferson.
from Deer Lodge from Jefferson
21 November 1867 · Mont. Terr. Laws 1867, 4th leg., p. 101
1868
Renamed Edgerton renamed Lewis and Clark; legislation used the spelling "Lewis and Clarke". Act passed 20 December 1867; took effect 1 March 1868.
formerly Edgerton
1 March 1868 · Mont. Terr. Laws 1867, 4th leg., p. 130
1872
Changed Choteau (now Chouteau) attached to Lewis and Clark "for judicial purposes."
ChoteauChouteau
4 January 1872 · Mont. Terr. Laws 1871, 7th leg., ch. 77/p. 585
1872
Boundary clarified Lewis and Clark boundaries redefined (no change).
no change
12 January 1872 · Mont. Terr. Laws 1871, 7th leg., ch. 20, sec. 6/pp. 430-431
c. 1879
Changed Choteau (now Chouteau) fully organized, detached from Lewis and Clark.
ChoteauChouteau
31 December 1879 · History of Montana 1739-1885, p. 494
1887
Boundary clarified Lewis and Clark boundaries redefined (no change).
no change
1 March 1887 · Mont. Terr. Laws 1887, 15th leg., sec. 735/pp. 835-836
1887
Lost territory Lewis and Clark lost to creation of Cascade. Act passed 12 September 1887; took effect 19 December 1887.
to Cascadeto Lewis and Clarke
19 December 1887 · Mont. Terr. Laws 1887, 15th leg., ext. sess., pp. 105-109
1889
Became part of Montana Lewis and Clark 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
1897
Gained territory Lewis and Clark gained from Broadwater, Cascade, and Meagher.
from Broadwater from Cascade from Meagherfrom Lewis and Clarke
5 March 1897 · Mont. Laws 1897, 5th leg., pp. 53-55
1899
Gained territory Lewis and Clark gained from Deer Lodge. Act passed 28 February 1899; took effect 1 June 1899.
from Deer Lodgefrom Lewis and Clarke
1 June 1899 · Mont. Laws 1899, 6th leg., pp. 44-47
1903
Lost territory Lewis and Clark lost to Powell.
to Powellto Lewis and Clarke
6 March 1903 · Mont. Laws 1903, 8th leg., ch. 106/pp. 196-197
1905
Lewis and Clark County created Spelling of Lewis and Clark officially established as "Clark," not "Clarke."
from Clarkfrom Clarke
10 February 1905 · Mont. Laws 1905, 9th leg., ch. 13/p. 28
1921
Changed Part of Lewis and Clark boundary with Cascade placed on federal land survey line according to the Cascade boundary description; change was not reflected in Lewis and Clark description (no change).
Cascade
1 June 1921 · Mont. Rev. Code 1921, secs. 4311, 4328/pp. 1563, 1586-1587
1941
Exchanged territory Lewis and Clark exchanged small areas with Cascade.
with Cascade
28 February 1941 · Mont. Laws 1941, 27th leg., ch. 58/pp. 89-93

Land and parcels

What the maps cover in Lewis and Clark

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

Parcels Good enough

Lot lines and tax-map numbers for 40,293 parcels. Drawn for tax purposes: usually within a few feet of a survey, but not a survey.
checked 15 October 2026
Address points Official

One point per address, 45,121 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

Lewis and Clark by the Census

Population

70,973 2020 Census count

Housing units

33,599 2020 Census count

Land area

3,458 square miles

Water area

39 square miles

People per sq mi

21 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.

Records

Clerk of court: deeds and plats 406-447-8222from lccountymt.gov · checked 13 October 2026

Permits

Health department: septic and well 406-447-8351from lccountymt.gov · checked 13 October 2026
Septic Systemsfrom lccountymt.gov
Catering Permit - Lewis & Clark Countyfrom lccountymt.gov
Permits - Lewis & Clark Countyfrom lccountymt.gov

Zoning and code

Resolutions and Ordinances - Lewis & Clark Countyfrom lccountymt.gov
Zoning - Lewis & Clark Countyfrom lccountymt.gov

GIS and maps

County GIS and maps 406-447-8367from lccountymt.gov · checked 13 October 2026

County government

County government
The official website of Lewis and Clark County.
lccountymt.gov

See your own lot on these maps

Open Lewis and Clark 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 Lewis and Clark County

When was Lewis and Clark County founded?: Lewis and Clark County was founded in 1865, formed from Choteau County, Chouteau County and Jefferson County, and named after William Clark and Meriwether Lewis.
What is the county seat of Lewis and Clark County?: The county seat of Lewis and Clark County is Helena.
Is there an online parcel map for Lewis and Clark County?: Yes. A public source publishes a parcel map of 40,293 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Lewis and Clark County's boundary or name changed?: Lewis and Clark County was created in 1865 from Choteau County, Chouteau County and Jefferson County. Since then the Atlas of Historical County Boundaries records 12 later changes, chiefly involving Lewis and Clarke County, Cascade County and Choteau County. It was formerly called Edgerton.
Who issues building permits in Lewis and Clark County?: The county's page on building permits: Catering Permit - Lewis & Clark County. Inside a city or town, ask that city first.
Who issues septic and well permits in Lewis and Clark County?: The county's page on septic systems and wells: Contact Public Health.
Is my lot in a flood zone?: We do not have flood maps for Lewis and Clark County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby