The Doud book is

"Doud-Dowd and Allied Families" by O.L. Doud 1976. It is out of print but some libraries have it. It expands on the previous genealogy published in the 1880's. Not perfect by any means but a great place to start. It covers quite a few lines (including Iowa) all the way back to Henry Doude and Elizabeth (now known to be Dadson).