I believe the Jacob Montag (b. 1813/14 in Germany) that you mentioned is the father of Ignatz. If you have access to Ancestry's records, check the 1860-1870-1880 censuses for Jacob Montag and family. They were living in Trenton, Washington Co, Wisconsin.

Interestingly, Jacob Montag lived next door to Adam and Ernestine Laufer on the 1860 and 1870 censuses. It is believed, but not known for certain, that Adam Laufer's mother was a Montag. So Jacob may be a cousin of Adam Laufer. The Montags may have come from a small town in Thuringia, Germany called Wendehausen.