William Augustus Prentiss (March 24, 1799 – November 10, 1892) was an American merchant, Republican politician, and Wisconsin pioneer.

Prentiss received a common school and academic education, and went to work in mercantile pursuits.

In 1822, he went to live with his other brother, Samuel Prentiss, in Montpelier, Vermont, where he began his own mercantile business.

He quickly formed a partnership with Lemuel W. Weeks to operate a general merchandise store in the Juneautown area.

[1] Prentiss was technically only the second justice of the peace in the Wisconsin Territory, the other located in the Green Bay area.

That same year, he was elected to the board of trustees of the village of "Milwaukee on the east side" (Juneautown).

[1][6] The Democratic administration after him let by Herman L. Page, was very hostile toward him, and lying in their attempts to prove him bad.

[8] He was said to be a tall and stout man, with a large head, light brown hair and blue eyes.

[3] Prentiss largely retired from public life in 1872, but still made occasional appearances at party gatherings or civic events.