Iowa-set fiction tends to do one of two things: render the small-town landscape with stubborn affection, or use the state as the empty centre against which something larger plays out. Either way the best of it is worth reading before you come.
Gilead by Marilynne Robinson. Set in the fictional small town of Gilead, Iowa, this Pulitzer-winning epistolary novel takes the form of a dying minister's letter to his young son. It is the great novel of Midwestern Protestant interior life — slow, generous, and unsentimental — and the eastern Iowa landscape is everywhere in it. The follow-ups (Home, Lila, Jack) are equally good.
A Thousand Acres by Jane Smiley. Smiley relocates King Lear to a thousand-acre Iowa farm in the 1980s and writes one of the best American novels about land, inheritance, and family secrets. The descriptions of the fields, the equipment, and the rhythms of farming are unimprovable, and the moral weight lands hard.
The Bridges of Madison County by Robert James Waller. Famous to the point of mockery, but worth reading: a thin, romantic novel about a four-day affair between a National Geographic photographer and a farm wife outside Winterset, just southwest of Des Moines. The covered bridges it made famous are still there.
Some Luck by Jane Smiley. First in Smiley's Last Hundred Years trilogy, this multigenerational saga begins on an Iowa farm in 1920 and follows a single family through the century. The detail is overwhelming in a good way; you finish the trilogy with a clear sense of how the Midwest got from horse-drawn ploughs to industrial agriculture.
The Music Man by Meredith Willson. Set in fictional River City, Iowa (modelled on Willson's hometown of Mason City), the libretto and lyrics are a love letter to early-twentieth-century Iowa small-town life. Read it before you watch any of the productions; the affection is more visible on the page.