Milton Speer "Mit" Simms, son of Maria Louisa Speer and Franklin Robert Simms, was born in Rockford, Alabama in 1873 and grew up there. He moved to Arizona Territory sometime before 1902. On December 25, 1902, he married his first wife, Lillian Mary McCabe (1881–1941). No children emerged from this marriage.

The Arizona State Treasurer is the state of Arizona’s chief banker and investment officer. The Treasurer’s Office accounts for and manages the cash flows of state government, directs the state’s banking services, disburses public funds, and manages Arizona’s investment portfolio. The state treasurer also serves on the management boards of a number of public entities. The state treasurer is one of six statewide elected officials and serves a term of four years. A person may only serve as state treasurer for two consecutive terms. The Treasurer is third in the line of succession to the office of Governor of Arizona.