I am trying to locate any information on my great grandfather. I have his death certificate and have tracked him from 1880 US Census on, but nothing before. Believe I found him in 1870 in Milwaukee, WI but nothing to prove it is him.

According to 2 different US census- he immigrated either in 1849 or 1851 from Hesse Darmstadt. Death certificate says father was George Knapp and unknown mother. He was Catholic as he was buried in a Catholic cemetery in Mineral Point, Wisconsin.

born in Hesse Darmstadt 14 April 1840 or born April 1842
Married Maria Catherine Schmitz born 9 Jan 1850 in Prussia - Believe in area of Cologne (Koln), Nordrhein-Westfalen, Germany which was part of Prussia at that time.

All their children were born in Wisconsin so believe they met most likely in Milwaukee, Wisconsin.

Looking for location of birth, date of birth, parents, and any further info that could be provided