In May of 1903 Gustav Ruecker, F.W. Bandlow, William Briemann, Charles Thorn, J.P.Stoye, Moritz Lehner, Fred Greiner, William Milbrot and Charles Gutenschwager incorporated Theresa Bank with the charter being issued in 1905. On April 14, 1905, Theresa State Bank opened its doors in a small room located in the Grand Central Hotel, in the building that is now a local establishment in Theresa. In 1910 Theresa State Bank built a new building on Milwaukee Street (now the Village Hall). This location was in service until 1975 when the current building in Theresa was erected.

Gustav Ruecker was president from 1903 until 1941 and was succeeded in office by F.A. Bandlow, son of originator F.W. Bandlow. He served until 1953 when Dr. Arnold Boegel became president. In 1986 Robert O. Baker took over the helm, followed by Susanne Press from 1992 until 1994. Thomas O'Connor led the organization for several months until Michael Bonnett was hired as president and he served as the chief executive officer until January 2008. Russell Turk, who started with the organization in 1999, now leads the bank as President and Chief Operating Officer.

In 1996 a new main office of Theresa State Bank was put into operation in Lomira. In February, 1999, Theresa State Bank officially changed its name to TSB Bank. Another branch opened in Mayville in July, 1999. 2005 marked the 100th anniversary of TSB Bank.