Thank you so much for your lengthy, and informative, response. Your insight is helpful.
I believe that our ancestor came from the Posen area because of the obituary that ran on him. Of course, the obituary is only as good as the source providing the information, but I don't have much else to go on! From the 1880 census, he was listed as being from Prussia. Unfortunately the 1875 state census does not list either his country of origin or his immigration/naturalization date. Like I said in my previous message, he purchased his land in 1866 -- I do know this for sure! His death certificate did not list his parents, and simply listed Germany as his country of origin.
The John Leitz you have found appears to be of the same age as our ancestor, although I had believed that his wife came with him and that he had some children with him as well (the 1880 census lists some of his children as having been born in Prussia). The reference librarian up in Fond Du Lac, Wisconsin, found the same information you have. I have been able to order the microfilm (after a minor hiccup) from the FHC, and hope that it will arrive within the next 3 weeks. If this is not him, I'm not exactly sure how to go about finding when, how and from where he came.
Thank you for the information on the birth records in Germany. The town data would be on the passenger ship list, but here's a quick question: how would I know from which church to order the birth records? I would think that there would be multiple churches in each town. I suppose I could just keep going until I hit the right one.
As far as the immigration/naturalization is concerned, that's another gray area for me as I've never researched these records before. I sent a request to the Fond du Lac county library who does this research for free (this is the county in which he bought his property); however, they didn't find anyone with the various spellings of the last name in that county. They did find an individual in the county just to the north, but the nationality is listed as Austria, and I fear that it's not the one and the same person. In addition, the immigration year is pretty far off. If I don't know the port that he came to, or if he got his naturalization/immigration paperwork elsewhere, how would I track him down? I sorely need some sort of index to the immigration/naturalization records, but I don't believe there's one out there.
In other words, if the FHC passenger list turns out to NOT be my guy, I don't know where to turn to next. Do you have any ideas? Or have I hit the proverbial brick wall?