Hit a Brick Wall with My 3rd Great Grandfather Henry Vennekolt

My 3rd Gr. Grandmother- Mary (Bicker) Vennekolt remarried 22 Aug 1862 as Mrs. Mary Venneholt to Herman S. Carter Sr., but have not been able to find more information on Henry Vennekolt 1818 Germany- arrived in US about 1850.
Mary and Henry had at least three (maybe more) children: Maria Frances (Vennekolt)Koerner 1852, Martha (Vennekolt) Ludeke 1854, and Henry Vennekolt 1859.
Mary and Herman had at least two children: Herman Jr. 1864, and Henry Carter 1867.
They came from Germany, but resided in Freeport, Stephenson, Illinois.