October 25, 1836
The first legislative assembly of Wisconsin Territory convened at Belmont, organized by electing Henry S. Baird president of the council; Governor Dodge by proclamation declared the members duly elected.
The evidence
“The first session of the Legislature, in 1836, by a proclamation of General Dodge, who was the first Governor, was convened at Belmont, now in Lafayette county, on the 25th day of October, of that year. The second session was held at Burlington, now in the State of Iowa, November 6th, 1837, at which session the seat of Government was located at Madison, where the third session of the Legislature was held November 26th, 1838.”
1856-history-of-rock-county/01-wisconsin.md, PDF p. 21 / book p. 3
Guernsey, Orrin, and Josiah F. Willard, editors. History of Rock County, and Transactions of the Rock County Agricultural Society and Mechanics' Institute. Janesville, Wis.: William M. Doty & Brother, 1856. Cornell University Library via the Internet Archive, archive.org/details/cu31924028871593.
Grade A: Found on a page of one of our sources
On the printed page (PDF p. 21 / book p. 3) · open the whole page “On October 25, 1836, Governor Dodge, by proclamations, declared duly elected members of the council and of the house of representatives, the persons for whom a majority of votes had been cast at such election, and on the same day the first legislative assembly of Wisconsin convened at Belmont, in what was then the county of Iowa, but now the county of LaFayette, and organized by the election of Henry S. Baird as president of the council, and Peter H.”
1908-brown-rock-county/05-historic-evolution.md, Vol. 1, PDF p. 132 / book p. 118
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
On the printed page (Vol. 1, PDF p. 132 / book p. 118) · open the whole page “slature when it met at Belmont in 1836. Belmont, the Birthplace of Wisconsin Territorial Government The First Capitol Historic Site lies a mile or two northwest of the small village of Belmont. This is where the first territorial legislature established Wisconsin’s territorial government. These lawmakers, huddled in the cold during the fall and winter of 1836, built the framework that would evolve into the state of Wisconsin 12 years later. They met from October 25 to December 9, 1836. In that time, they put 42 laws on the books, established a judicial system, called for roads and railroads, and – most significantly – established Madison as the permanent capital city. Townsfolk outside of the First Wisconsin Capitol Building Capitol Relocation Affects Belmont’s Livelihood Establishing Madison as the capital city had a profound and immediate impact on the Belmont community, as numerous people and several businesses lef”
https://firstcapitol.wisconsinhistory.org/explore/history-first-capitol/
firstcapitol.wisconsinhistory.org, https://firstcapitol.wisconsinhistory.org/explore/history-first-capitol/
Grade B: Found on an institutional web page