I have researched for over 25 years in the Morristown area where the two families came together with the marriage of Bill Dempsey and Peggy Gannon in 1949. It has been ironic how the two families lived on the same streets and yet it wasn't until that marriage that it all came together. The Dempsey's fought in all the wars since the Civil War. The Gannon's have been more involved with telegraph, telephone and electronics. I have walked all the battlefields that BW Dempsey fought in the Civil War and now live near Annapolis where he came after being in Andersonville as a POW in 1864-65. He then came to Parole, which is down the street from me now. There is a letter from his wife Catherine, in the National Archives asking for a pension in 1879 after he died from TB after being one of the first marshalls in Morristown.
I have been successful going back to all 16 gr. gr. grandparents and have information about their occupations, residences and parents' birthplaces. I would like to establish some links in Ireland but have not been successful.
I have made many trips to the National Archives in Washington, D.C., New Jersey State Archives, Morristown, NJ library, Civil War battlefields including Gettysburg as well as trips to visit aging relatives who have some important information, documents, photos and memoriabilia.
The Gannons have 2 gr. gr. grandparents from Bavaria, Germany. They were the Rodlers and for a brief time in the late 1800's owned several grocery, crockery and general stores on the "Green" of Morristown, but they also traveled back to Germany in 1872 which was reported in the papers. They also had numerous residences and seemed to be somewhat wealthy.
The Gannons have had a family reunion every summer in Lewis-Morris Park in Morristown for the last 10-12 years and has usually been well attended. I always bring the pedigree chart for the neices and nephews, aunts and uncles, brothers and sister and the numerous cousins to check out and refresh.
The Dempseys/Gannons still live the north NJ area but as expected some have moved away-including myself to Maryland but the majority still live in that area.
I continue to do this research but have been frustrated because I have not been able to come up with any more leads, especially overseas help. The Dempsey's came from Carlow Co and it seems the Gannons' from County Cavan in Ireland but getting good leads is hard.