Fall 1836
Erastus Giles came from Roscoe, Illinois, to Rock County and helped raise the first house put up in Beloit; he is registered as settling in Turtle in October 1836.
The evidence
“P.O.Beloit; born in Windsor Co., Vt., Oct. 3, 1816; son of Joshua Giles, a prominent farmer who moved to Michigan, with his family, about 1833 ; he died the year following, aged about 54. Erastus came to a place now called Roscoe, in Illinois, in 1836, and in the fall of same year went to Rock Co., Wis. ; helped to raise the first house put up in Beloit. About 1840, settled on 240 acres in Turtle ; started for California in 1851 ; took a year to get there; was there seven years.”
1879-history-of-rock-county/23-bios-turtle.md, PDF p. 800 / book p. 804
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
“Egery, Vermont, Turtle, July, 1837 ; Erastus Giles, Vermont, Turtle, October, 1836 ; Henry Tuttle, New York, Clinton, October, 1837 ;”
1908-brown-rock-county/31-smaller-cities-villages-towns.md, Vol. 2, PDF p. 206 / book p. 710
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