Plainfield’s post office opened in 1849, and 10% of its homes were built before 1940
How Plainfield began
When was Plainfield founded?
The Plainfield post office opened in 1849, the earliest record of the town by name.
Questions about Plainfield’s history
What year was Plainfield founded?
The Plainfield post office opened in 1849, the earliest record of the town by name (U.S. post office records).
Memory lane
What the archives can’t tell you, neighbors can.
Where this page comes from
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). How TownRatings grades history →