Thermopolis’ post office opened in 1895, and 18% of its homes were built before 1940
More historic than 70% of U.S. towns · #9 of 28 in Wyoming. What drives it
5 places in town are on the National Register, among them a historic district with 15 buildings. Below: 5 old photos and papers, maps from 1907 on, and the census since 1900.
Founding year: the first Thermopolis post office (Blevins & Helbock, CC0).
History grade
What drives Thermopolis’ History grade
On its age, its old homes and the National Register, Thermopolis is more historic than 70% of U.S. towns, #9 of 28 in Wyoming. Its National Register listings hold the grade up; its age pulls it down.
B+
HistoryA character grade: shown, never part of Thermopolis’ overall grade.
Wyoming towns list more on the Register than most of the country (a typical Wyoming town has 25.1 per 10,000 residents, the U.S. 2.4), so Thermopolis’ 81.2 sits above most of its state (82% of Wyoming towns have fewer) while its 22 historic buildings outnumber those of 80% 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 (±7.6 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 Thermopolis’ past
Read from the archive, the National Register and the record. The page puts what stands out first.
Peaked at 3,955 in 1960; 2,725 people lived here in 2020.
13 censuses, 1900–2020.
U.S. Census Bureau decennial counts, from the census table on Thermopolis’ Wikipedia page.
Every building
Thermopolis, building by building, 1907–1918
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.
National Park Service, National Register of Historic Places. Photos from Wikimedia Commons, credited on each place’s page.
The story so far
Thermopolis, in brief
Wikipedia doesn’t have a history of Thermopolis yet. The photos, dates and memories neighbors add here are how it gets written.
Thermopolis is the county seat and most populous town in Hot Springs County, Wyoming, United States. As of the 2020 census, Thermopolis had a population of 2,725. Thermopolis, Greek for "hot city", is the location of numerous natural hot springs, in which mineral-laden waters are heated by geothermal processes. The town claims the world's largest mineral hot spring, "The Big Spring", as part of Hot Springs State Park. The springs are open to the public for free as part of an 1896 treaty signed with the Shoshone and Arapaho Indian tribes.
Its first post office opened in 1895. Between the 2010 and 2020 censuses its population fell from 3,009 to 2,725 (-9%).
Intro from Wikipedia. Population: U.S. Census Bureau.
Timeline
Thermopolis, 1895 to 1968
Woven from the archive, old maps, post office records, the National Register and the people born here.
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.
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.
The Thermopolis post office opened in 1895, the earliest record of the town by name (U.S. post office records).
How does Thermopolis rank for history?
Thermopolis is more historic than 70% of U.S. towns, #9 of 28 in Wyoming. 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 Thermopolis?
5 listings: 4 buildings, among them the US Post Office-Thermopolis Main (listed 1987, the first), and 1 historic district, the Downtown Thermopolis Historic District, with 15 contributing buildings. 22 historic buildings in all.
How old are the homes in Thermopolis?
18% of Thermopolis’ homes were built before 1940 (Census estimate, ±7.6 points), against a typical 12% for a Wyoming town; the median home was built in 1966.
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 (5), Wikidata (1), the National Register of Historic Places (5), Wikidata and Wikipedia for famous people, 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.
1918
1918
1968
