Old original books and images are wonderful, but digital versions have many advantages. You can print on demand, save, export, share, zoom, etc. The David Rumsey Historical Map Collection allows you to do this with the 1875 Illustrated Historical Atlas of Iowa, published by Andreas Atlas Company.
Print copies are available for viewing at the Des Moines Public Library locations (dependent upon condition). Pages focusing on Polk County can be viewed here.
David Rumsey donated his collection to Stanford University earlier this year, but maps will continue to be added.