I asked about the RICH and FLANIGAN names, because I understood your earlier post to mean that both of these names are mentioned in the letters.Sorry for the confusion.
The Rich name probably has a Jennings County connection, but Flanigan might not.Ann Kearney O'Neil/Rich/Warner was a sister to Catherine "Serene" Kearney (born about 1830 in New York) who married a John FLANIGAN [FLANAGAN and other var.], probably in Erie, Pennsylvania.That's where Serene and John Flanigan ended up, anyway.
When I saw the surname in your list, I had hoped that maybe the two sisters had come out to Indiana together and that Serene maybe had met John Flanigan there, or that maybe Serene and John had been mentioned when they came to visit sister Ann some time.
I know the Flanigan name was a long shot.The timeframe for "my" John Flanigan, and yours, is not bad, but I think mine was in Pennsylvania by 1860, or so.Do you have any other background of "your" John Flanigan that might place him in Erie, Pennsylvania?