The area's first known inhabitants were the native Coast Miwok and Pomo peoples. The town currently sits atop multiple village sites. The town of Sebastopol formed in the 1850s with a U.S. Post Office and as a small trade center for the farmers of the surrounding agricultural region. As California's population swelled after the westward migration and the California Gold Rush of 1848–1855, more and more settlers drifted into the fertile California valleys north of San Francisco to try their hand at farming.