Throughout the 1890s, private banking institutions sporadically served Mason residents. In December 1903, several pioneer settlers met to form a new bank. It received its authorization in January 1904 as the German American National Bank of Mason.
John Lemburg, Sr. served as the first president, J.W. White as vice-president and F.W. Lemburg as cashier. During the bank's first 100 years, six other men would serve as president, including J.W. White, who served two different terms.
Anti-German sentiment during the First World War caused the bank board to change the bank's name in 1918 to Mason National Bank. The institution led the community in purchasing Liberty Bonds during the war. In 1932, amid the Great Depression, the First State Bank of Mason merged into the Mason National Bank. J.D. Eckert, formerly of First State Bank, became president. That same year, the bank received certification by the Federal Deposit Insurance Corporation. In 1934, Eckert retired, and White resumed the position of president until his death in 1939. D.F. Lehmberg followed him in the office, remaining until his death in 1953. Following Lehmberg's death, Wilburn "Bill" Lemburg (d. 1972), grandson of John Lemburg, Sr., became the bank's president. Under his leadership, the bank moved in 1968 from the north side of the town square to the present
location, previously the site of his grandfather's house.
Throughout its history, the bank's leaders have been active in local organizations. Mason National Bank is well-known and respected for its generous support of community programs.