In 1836, he traveled south to the area that is now Fond du Lac, Wisconsin, and conducted the first plat for a village at that site.
During these years, he also often served as a justice of the peace, and, in that capacity, he performed the first marriage held in Fond du Lac County, between Alonzo Raymond and Harriet Pier, a niece of Fond du Lac pioneer Edward Pier.
During those years, Bannister was active in the Free Soil Party and was a member of the state central committee in 1849.
In the general election, Bannister came in a distant third place behind Democrat Samuel Beall and Whig Timothy O.
[5] Over the next several years, Bannister was involved in several large business projects in the city, including banks and railroads.
Through his mother's family, John Bannister is a descendant of Thomas Nash, who emigrated from England to the Connecticut Colony sometime before 1640.
John's younger brother Henry M. Bannister was a scholar at the Garrett–Evangelical Theological Seminary and one of the leading Methodist theologians of his era.
Theodore, after residing briefly with Bannister in Fond du Lac, apprenticed as a surveyor under Albert Gallatin Ellis and became one of the first inhabitants at what is now Appleton, Wisconsin.
His son, John A. Bannister, was the first American child born in Fond du Lac County, on June 20, 1839.