Thomas Fallon (1825–1885) was an Irish-born, Canadian-raised American capitalist and politician, the tenth Mayor of San Jose, California.
Fallon's family moved to Canada when he was a child. When he was 18, he moved to Texas, where he joined the third expedition of John C. Frémont to Alta California. Early in 1846, Fallon stayed in Santa Cruz after Frémont visited the area. In June 1846 he joined the Bear Flag Revolt, raised a group of 22 volunteers in Santa Cruz, and appointed himself captain. The force crossed the Santa Cruz Mountains to capture the Pueblo of San José without bloodshed, on July 11. On July 14, 1846 he received an American Flag from Commodore John D. Sloat, which he raised over the juzgado of San Jose, the pueblo's administrative building. Fallon's force then joined Fremont's California Battalion for the remainder of the Mexican-American War.
After the war, Fallon returned briefly to San Jose, then back to Santa Cruz where he established a business as a saddler. At the beginning of the California Gold Rush in 1848, Fallon took a cargo of iron picks made in Santa Cruz to sell to the gold miners. With his share of the profits, he built a combination residence/workshop/hotel on the Mission plaza in Santa Cruz. In 1849, he married Carmel (Carmelita) Castro Lodge (1827–1923), daughter of local landowner Martina Cota Castro (1807–1890) and her husband Michael Lodge, owners of Rancho Soquel.