1837
The first large building in Beloit, a temporary lodging and boarding house, was made for the men building Blodgett's mill.
BeloitGrade A · 1 independent source
The evidence
“Here may titly be noted some of the first things of Beloit. The first large building erected was a temporary structure, a big lodging and boarding house, made in 1837 for the men who were building Blodgett's mill. It stood on ground now occupied by the Milwaukee & St. Paul railroad, next south of where the Beloit house was afterwards built, and in it, September 10, 1837, Professor Whitman, formerly of Madison university. New York, a Baptist minister from Belvidere, 111., conducted the first public preaching service in the settlement, preaching morning and afternoon two most lugubrious sermons from Genesis 47 :9 and Job 4:1.”
1908-brown-rock-county/06-history-of-beloit.md, Vol. 1, PDF p. 167 / book p. 151
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