Lionel M. Jacobs and Barron M. Jacobs were brothers, merchants, and bankers; sent to Tucson, Arizona, in 1867, to establish a retail store in association with their father, Mark I. Jacobs of San Francisco. First called the M.I. Jacobs and Co., the name was changed to the L.M. Jacobs and Co. after 1875. They closed the store in 1880, because of their growing involvement in banking; in 1879, they had established the Pima County Bank, the first bank in Tucson. They later became associated with the Cochise County Bank of Tombstone, known before 1882 as the Agency Pima County Bank; also the Arizona National Bank, first called the Santa Cruz Valley Bank.

Collection includes cancelled checks, drafts, invoices, receipts, weigh bills, stationery letterheads (business), letters and miscellaneous items pertaining to the mercantile and banking businesses of Barron Jacobs, 1874-1936, and his brother, Lionel Jacobs, 1841-1922, in Tucson and Southern Arizona.