John,
I just recently found the birth record of Koert Roskamp Eissen (sometimes spelled Aissen or Aeissen) in Weenermoor, Germany. He was born August 11, 1858 to Harm Berends Aissen and Hilberdina Roskamp, hence the middle name of Roskamp. Harm died around 1860 and Hilberdina remarried to a Jan Dirks Roskamp. Those two reasons could be why Koert had the last name of Roskamp by the time he came to the US. This Hilberdina is the sister of the John Roscamp that I have been searching for. Hilberdina was born in St. Georgiwold, Germany-not too far from Weenermoor. I am hoping to search the church records for that area soon.