San Dimas’ post office opened in 1888, and 1 of its places is on the National Register
More historic than 38% of U.S. towns · #245 of 847 in California. What drives it
Most of San Dimas was built recently: 5% of its homes predate 1940 and the median home dates from 1976. Its Register listing is the San Dimas Hotel. Below: 2 old photos and papers, maps from 1894 on, and the census since 1970.
Founding year: the first San Dimas post office (Blevins & Helbock, CC0). Wikidata: 1960.The full story ↓
History grade
What drives San Dimas’ History grade
On its age, its old homes and the National Register, San Dimas is more historic than 38% of U.S. towns, #245 of 847 in California. Its National Register listings hold the grade up; its share of homes from before 1940 pulls it down.
C+
HistoryA character grade: shown, never part of San Dimas’ 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 San Dimas’ 0.3 sits above most of its state (67% of California towns have fewer) while its 1 listings outnumber those of 51% of U.S. towns.
How sure. Graded on any two of the three inputs instead, the letter would range from C to C+. The pre-1940 share (±1.7 points) is firm at this size. The founding year is the first post office, not a stated founding date; Wikidata gives 1960.
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 San Dimas’ past
Read from the archive, the National Register and the record. The page puts what stands out first.
The first known European exploration of the area was in 1774, when Juan Bautista de Anza passed through on the first overland expedition of Las Californias, from New Spain-Mexico towards Monterey Bay. The area was originally developed in 1837 with the Mexican land grant from Governor Juan Bautista Alvarado to Ygnacio Palomares and Ricardo Vejar for the Rancho San Jose, then in Alta California. It later became known as La Cienega Mud Springs, so named because of local mud springs that created a riparian marsh and healing place. Palomares and Vejar conducted sheep and cattle operations on Rancho San Jose, also growing crops for consumption by the residents of the rancho. In the early 1860s, a severe drought decimated the ranch's population of sheep and cattle. Ygnacio Palomares died in 1864, and his widow began selling the ranch land in 1865. Vejar lost his share by foreclosure to tw…
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 San Dimas post office opened in 1888, the earliest record of the town by name (U.S. post office records). Wikidata gives 1960.
How does San Dimas rank for history?
San Dimas is more historic than 38% of U.S. towns, #245 of 847 in California. 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 San Dimas?
One place: the San Dimas Hotel (listed 1972).
How old are the homes in San Dimas?
5% of San Dimas’ homes were built before 1940 (Census estimate, ±1.7 points), against a typical 3.4% for a California town; the median home was built in 1976.
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), the National Register of Historic Places (1), Wikipedia, 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.
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