I'm also researching Mertens in Missouri. Henry John Mertens, b. 1823 "near Koln [Cologne]" according to a family record, m. Margaret Barbara Smith in Cooper Co, lived in Saline County MO. I found an obit in family records of Theodore W. Mertens, who had a coal and ice company in St. Louis. Wonder if he could be a brother or half-brother of Henry John. What I really need to find is H.J.'s home town in Germany--"near Cologne" is too vague. Do you have any Mertens information that might help? Thanks.