I don't know if our Oldenburgs are related. My great grandmother was Charlotte Antoinette Oldenburg. She married Frederick Dieterick Dohrmann in 1865, presumably in Landesbergen, Hanover, Germany.She was born May 15, 1843. Their first two children were born in Landesbergen--the rest in the Iowa and Illinois (they declared U.S. citizenship in 1876). I'd always assumed she was from Landesbergen, but I'm not sure. Did your relative have any siblings?