3 places in town are on the National Register, among them a historic district with 13 buildings. Below: 4 old photos and papers, maps from 1892 on, and the census since 1880.
The Boulder post office opened in 1871, the earliest record of the town by name. Another post office, Boulder Valley (1866), opened inside today’s city and later closed.
First census: 214 in 18802020 census: 1,201155 years
How historic is Boulder?
B+
More historic than 69% of U.S. towns, on its age, its old homes and the National Register.
Founding year: the first Boulder post office (Blevins & Helbock, CC0).The full story ↓
History grade
What drives Boulder’s History grade
On its age, its old homes and the National Register, Boulder is more historic than 69% of U.S. towns. Its National Register listings hold the grade up; its age pulls it down.
B+
HistoryA character grade: shown, never part of Boulder’s overall grade.
Montana towns list more on the Register than most of the country (a typical Montana town has 12.7 per 10,000 residents, the U.S. 2.4), so Boulder’s 117 sits above most of its state (81% of Montana towns have fewer) while its 15 historic buildings outnumber those of 78% of U.S. towns.
How sure. Graded on any two of the three inputs instead, the letter would range from B− to A−. The pre-1940 share is a Census survey estimate (±8.8 points). The founding year is the first post office, not a stated founding date.
Founding year: the first post office (other dates in Quick answers). Homes: Census ACS 2020–24. National Register: National Park Service, May 2026 list; each listing counted once (boundary changes and added documentation belong to their listing), and a historic district counts its contributing buildings. How TownRatings grades history →
What stands out about Boulder’s past
Read from the archive, the National Register and the record. The page puts what stands out first.
Lost a third of its people between 1930 and 1940, then more than doubled.
12 censuses, 1880–2020.
U.S. Census Bureau decennial counts, from the census table on Boulder’s Wikipedia page.
Every building
Boulder, building by building, 1892–1912
Fire insurance maps drew every building, what it was made of and what it was used for, so insurers could price the risk of fire. Pick a year, then a sheet.
Named for the many large boulders in the vicinity, the town of Boulder Valley was established in the early 1860s as a stagecoach station on the route between Fort Benton and Virginia City. It later became a trading center for nearby agricultural areas and the Elkhorn, Comet, and Baltimore mining districts. The Great Northern Railway branch line from Helena to Butte reached Boulder in 1888. State schools for the deaf, blind, and developmentally disabled were established in the city in 1892. In 1897, the town's name was shortened to Boulder.
Nothing in the archives for these yearsWeddings on Main Street, storms, parades, school pictures, the old store. If it’s in your family album, it belongs here.
Lost post offices, old corners and places now gone
Boulder had its own post office from 1871 to 1871. Another post office, Boulder Valley, opened and closed inside today’s town.
Boulder Valley
1866–1897
Boulder
1871–1871
Boulder
1897–today
18601940today
Hamlets and corners on the map
Mountain Valley Trailer CourtSunset Trailer Court
Gone or out of use
Boulderlocale
US Post Offices dataset (Blevins & Helbock, CC0). Places and cemeteries from the USGS Geographic Names Information System (2021).
Questions about Boulder’s history
What year was Boulder founded?
The Boulder post office opened in 1871, the earliest record of the town by name (U.S. post office records).
How does Boulder rank for history?
Boulder is more historic than 69% of U.S. towns. The History grade combines the town’s founding era, the share of homes built before 1940 and its National Register listings. It’s a character grade, so it isn’t part of the overall grade. How it works.
What is on the National Register in Boulder?
Three places: the Jefferson County Courthouse (listed 1980), the Montana Deaf and Dumb Asylum (1985) and the Montana State Training School Historic District (2014).
How old are the homes in Boulder?
19% of Boulder’s homes were built before 1940 (Census estimate, ±8.8 points), against a typical 13% for a Montana town; the median home was built in 1971.
Founding dates: Wikidata, Wikipedia, the U.S. post office records of Blevins & Helbock (CC0) and the Census. Homes by year built: Census ACS 2020–24. National Register of Historic Places: National Park Service (list of May 22, 2026). Old photos, postcards and papers: Wikimedia Commons, the Library of Congress and other public archives, credited on each item’s page. Maps: U.S. Geological Survey historical topographic maps (via Esri) and Sanborn fire-insurance maps (Library of Congress). History text and census tables: Wikipedia (CC BY-SA 4.0). Places that used to be: USGS Geographic Names Information System (2021).
From Wikimedia Commons (10), Wikidata (2), the National Register of Historic Places (3), Wikipedia, U.S. Geological Survey historical maps, U.S. Census counts (via Wikipedia), the US Post Offices dataset (Blevins & Helbock), the USGS Geographic Names Information System and Sanborn fire insurance maps (Library of Congress). Archive images are copied here with their credits and licenses, shown on each photo’s page. Refreshed monthly.
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