from Wikipedia:
“Iowa’s population is more urban than rural, with 61 percent living in urban areas in 2000, a trend that began in the early 20th century.[59] Urban counties in Iowa grew 8.5% from 2000 to 2008, while rural counties declined by 4.2%.[72] The shift from rural to urban has caused population increases in more urbanized counties such as Dallas, Johnson, Linn, and Polk, Scott, at the expense of more rural counties.[73]
Iowa, in common with other Midwestern states (especially Kansas, Nebraska, North Dakota, and South Dakota), is feeling the brunt of rural flight, although Iowa has been gaining population since approximately 1990. Some smaller communities, such as Denison and Storm Lake, have mitigated this population loss through gains in immigrant laborers.[74]”
99% was an exaggeration.. But you kind of proved my point. More city dwellers, and urban voters tend strongly to dem.