September 15, 1855
A house of worship erected during the summer of 1855 was dedicated (the passages disagree: P80 says dedicated September 15; P163 says a new house of worship was dedicated in the latter part of 1855).
BeloitGrade A · 1 independent source
The evidence
“A. well organized and interesting Sunday School is maintained, having 160 volumes in the library. During the summer of 1855 their house of worship was erected, and on the 15th day of September was dedicated. It is built of wood, 29 by 52 feet, and cost, exclusive of tho lot, about $1500.”
1856-history-of-rock-county/25-city-of-janesville.md, PDF p. 186 / book p. 168
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. 186 / book p. 168) · open the whole page