Shade trees like maple and hackberry can readily live beyond 20 years.  If you saw decline or death in these trees in that time frame, it is likely the product of poor environmental conditions or poor planting/care.  
Emerald ash borer has caused the death of all ash trees across the state, and replanting ash is not recommended.

This link will take you to a publication that provides a list of trees that could replace those you lost. While the title says "Ash Alternatives" they are great trees for replacing any lost shade tree in Iowa (not just ash).
https://store.extension.iastate.edu/Product/14438
Use the information in this publication to pick a tree that is the best size, color, and shape and will tolerate the soil conditions in your area.

Below are a few more resources that can help be sure your new tree is planted and cared for as well as possible to allow it the best chance at success.
https://yardandgarden.extension.iastate.edu/how-to/tree-planting-basics
https://yardandgarden.extension.iastate.edu/how-to/care-newly-planted-trees

If you see issues with your new trees (or have other established trees that are declining), use these resources to help determine the cause of the problem.
https://yardandgarden.extension.iastate.edu/how-to/decline-newly-planted-trees
https://yardandgarden.extension.iastate.edu/how-to/causes-branch-dieback-trees
https://yardandgarden.extension.iastate.edu/how-to/how-diagnose-problems-trees-landscape