There's an important surplus in Iowa today-people. Our natural population increase (births) has always been greater than our natural decrease (deaths). Since the turn of the century there's been a net movement of surplus people out of Iowa into other areas.
Wakeley, Ray E.
"People- Iowa's No. 1 Surplus,"
Iowa Farm Science: Vol. 3
, Article 5.
Available at: https://lib.dr.iastate.edu/farmscience/vol3/iss2/5