Most of Thermal was built recently: 4% of its homes predate 1940 and the median home dates from 1977. Below: 1 old photo or paper and maps from 1941 on.
The Thermal post office opened in 1902, the earliest record of the town by name. Another post office, Kokell (1901), opened inside today’s town and later closed.
2020 census: 2,676124 years
How historic is Thermal?
D
More historic than 11% of U.S. towns, on its age, its old homes and the National Register.
Founding year: the first Thermal post office (Blevins & Helbock, CC0).The full story ↓
History grade
What drives Thermal’s History grade
On its age, its old homes and the National Register, Thermal is more historic than 11% of U.S. towns. Its National Register listings hold the grade up; its age pulls it down.
D
HistoryA character grade: shown, never part of Thermal’s overall grade.
Few California towns list much on the Register (a typical California town has 0.0 per 10,000 residents, the U.S. 2.4), so Thermal’s 0.0 sits below most of its state (31% of California towns have fewer) while its 0 listings outnumber those of 23% of U.S. towns.
How sure. Graded on any two of the three inputs instead, the letter would range from D to C−. The pre-1940 share is a Census survey estimate (±4.0 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 Thermal’s past
Read from the archive, the National Register and the record. The page puts what stands out first.
On December 30, 1823, Brevet Captain Jose Romero led a military expedition finding a route to Tucson from San Gabriel passes in the foothills west of Thermal and Martinez Indian Village (South of Thermal).
Thermal (originally Kokell) began as a railroad camp in 1910 for employees of the Southern Pacific Railroad, followed by Mecca (originally called Walters) in 1915 and Arabia in between, each with about 1,000 residents. Permanent dwellings were soon established on Avenue 56 (renamed Airport Boulevard), former U.S. Route 99 (State Route 86) and State Route 111 by the 1930s.
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 Thermal post office opened in 1902, the earliest record of the town by name (U.S. post office records).
How does Thermal rank for history?
Thermal is more historic than 11% 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.
How old are the homes in Thermal?
4% of Thermal’s homes were built before 1940 (Census estimate, ±4.0 points), against a typical 3.4% for a California town; the median home was built in 1977.
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 (7), the Library of Congress (1), Wikipedia, U.S. Geological Survey historical maps, the US Post Offices dataset (Blevins & Helbock) and the USGS Geographic Names Information System. Archive images are copied here with their credits and licenses, shown on each photo’s page. Refreshed monthly.
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