I am not related to this person, just got this page from the Wisconsin Historical Society for a different person, and thought I'd share the rest of the information on the page. Hope this helps!
Source: Wisconsin Necrology, Vol. 4, p. 107
Dr. J. L. Jenckes died at Hazel Green Wis Apr. 8, 1884 aged 68 years. He was born in R Island, and came to Wis 1848.