You have probably gotten these answers a bunch of times by now, but certainly the census, although the 1840 census will not give much info. Perhaps you already have 1850. Also look for Iowa State censuses, which were in the -5 years, although maybe not each decade. (i.e., 1845, 1855). If you know what church or denomination they were, look for the church records, as they would have baptismal & marriage records. Go to the County Courthouse,, as they may have some records, if I recall from those early years.The Dubuque City Directories did not start until 1857-8, but check those out as soon as they started. Even if you do not live near Dubuque, it will be worthwhile to contact or join the Dubuque Key County Gen. Society dckcgs@hotmail.com They have a newsletter, dues are small, and they have many resources. They Carnegie-Stout Library in Dubuque has all the City Dirs., a great Obit. card file, the State censuses, and the marriage indexes, which go back at least to 1860. Good luck, Jean