Summer 1833
Town lines were run by surveyors Mullett and Brink in the third quarter of 1833.
The evidence
“4th (luarter, 1833. Township Lines West of River Mullett & Brink M. T. Williams., July '.I, 1833 Robert T. Lytle 3d quarter, 1833. Township Lines East of River Mullett & Brink August 17, 1835 1st quarter, 1836.”
1879-history-of-rock-county/08-rock-county-ch02-mounds-indians-black-hawk-settlement.md, PDF p. 329
Butterfield, C. W., et al. The History of Rock County, Wisconsin: its early settlement, growth, development, resources, etc. Chicago: Western Historical Company, 1879. Cornell University Library via the Internet Archive, archive.org/details/cu31924028871585.
Grade A: Found on a page of one of our sources
“The United States began the surveys of this part of Rock county in the summer of 1833. The portion of the town of Janesville west of the river was first surveyed. The town lines were run by surveyors, Mullet and Brink in the third quarter of 1833, and the sections and subdivisions were surveyed later in the same year by George W. Harrison.”
1908-brown-rock-county/26-history-of-janesville.md, Vol. 2, PDF p. 10 / book p. 525
Brown, William Fiske, editor. Rock County, Wisconsin: A New History of Its Cities, Villages, Towns, Citizens and Varied Interests, from the Earliest Times, Up to Date. Chicago: C. F. Cooper & Co., 1908. 2 vols. archive.org/details/rockcountywiscon01brow, archive.org/details/rockcountywiscon02brow.
Grade A: Found on a page of one of our sources