William Justan Fisk (June 25, 1833 – March 1, 1909) was an American businessman, Republican politician, and Wisconsin pioneer.

He was a prominent banker in Green Bay and was one of the legislators responsible for the repeal of the railroad regulating Potter Law in 1875.

In 1849, he went to work for a jeweler and watchmaker, and the next year he was hired as a clerk for a Fort Howard merchant, earning $25 per month.

After that deal, Fisk erected a shingle mill in Fort Howard, which became his primary business interest for the next several years.

Fisk's company remained solvent, but was stuck with 2,000,000 unsold shingles, which he had to store at a warehouse in Chicago for two years until the supply could be entirely sold off.

He suffered a severe financial loss in 1871 due to Peshtigo fire, which destroyed about 10,000 acres of his timber land, but he doubled down on his banking interests.

He was elected to his first term in the Wisconsin State Assembly in 1874, running against the railroad regulations that had passed earlier that year.

[4] William Fisk married Mary J. Driggs at Fond du Lac, Wisconsin, on January 8, 1855.

[4] Mary's sister, Martha, married Samuel Ryan Jr., another important pioneer of the Fox Valley area and founder of the Appleton Crescent newspaper.