Katherine - My husband's great grandmother was Katherine Poss, born 1878 St. Louis, died 1940. (She married John Thuet, then Louis Stiehl.) Her parents were Daniel Poss born 1843 Germany, died 1880 St. Louis and Katherine Platt born 1840 Germany died 1908 St. Louis.
Daniel had a brother John (or Johann) Adam Poss b 1838 that also came to St. Louis.
I have a little more info on Daniel and John Adam's children. I think that their parents in Germany may have been Daniel Poss and Margaretha Will.
I live in St. Louis, too. Would love to compare notes!