The Joseph Wagner you are looking for was my greatgrandfather. He was a very early settler of the State of Wisconsin and served in the State's Territorial Legislature and ,for many years, as a State Senator. The woman you refer to, my great grandmother ( I believe her name was Katherine) was his second wife. Family lore says that she was his housekeeper, who he married following the death of his first wife. She was many yeare his junior. My grandfather (Albert Wagner) was the youngest, and only surviving male child, of this marriage (there were three or four daughters). Several others children died in early childhood. Family lore also holds that my great grandfather became a Lutheran when he married Katherine Diederich. Therefore I believe they would have been married in St. Paul's Church, which continues as the Lutheran church serving that area of Wisconsin to this day.
Both Katherine and Joseph are buried in Forest Home Cemetary which is located immediately North of State Hwy. 23 between the villages of Mt. Calvary and St. Cloud Wi.
It is very possible that Messrs. Fritz and Neis worked for him in that he was a major landholder. Early maps of Wisconsin show him owning more than 10,000 acres of land, some of which my grandfather inherited and continued to farm with hired help through about 1929.
I am fortunate to have many of Joseph Wagner's original papers including the 1929 ( I think) newspaper clipping announcing Katherine Wagner's death but would need to do some digging. I am really interested in this man and his life and am glad to have bumped into you,almost by accident.
Hope to hear from you soon.