As a historically Luxembourger community, St. Donatus, Iowa drew many new Luxembourger immigrants- which means that their records should show up in the records of the local Catholic churches. Many are of these records are not online, but some helpful hints to finding them are...
1) St. Donatus is still an active parish, as are the Roman Catholic churches of the area which also housed Luxembourger immigrants. If you're looking for a record, you may want to contact the parishes at http://www.stjosephbellevue.org/.
2) The Family History Library has microfilmed the local cemetery records. Iowa Genweb lists the microfilm numbers and a description at http://iagenweb.org/jackson/FHC/FHC_Cemetery.html. Verify the microfilm number before ordering the microfilm - the site dates from 2007.
3) St. Donatus actually has a parish museum containing artifacts from the early years of the parish and more importantly, genealogical records. Information on the museum can be found at http://www.luxamculturalsociety.org/StDonatusHeritageMuseum.htm.
I'm sure there is more online, and I'd love to hear what you've found.