My random 2cents from 50 years of generally sentient treks back to the ancestral lands (Fayette Co) plus Dubuque, Mt Vernon, and Ft. Dodge and in-between and beyond.
As noted, once upon a time there were many farms and many kids generated on those farms and those kids couldn't all farm and many didn't want to. Iowa historically educated their kids and had high literacy rates and sent their kids out into the world. Farms became fewer and bigger and there was even a move by farmer to live in "town" tiny places but tidy with a main street and simple businesses--mechanics and mills and the taps and if big enough a grocery store. As farms became fewer and people moved into towns most farm houses were torn down because that's valuable land they're sitting on. The tidy towns started to house former farmers and eventually fewer people and then started looking rough around the edges and then not so tidy and the main street went vacant and then the buildings fell and/or were torn down. Farmers that were left actually started living on farms again, though in much large complexes to hold their increasingly elaborate machinery and their houses looked fancy too. Of course these places are few and far between the unshiny remnants of towns and gives much of rural Iowa an almost feudal look to it.
Drugs were a problem even in rural areas
MethlandAnd there was a concern that all the smart people were leaving, leaving all the dumb ones behind
Hollowing Out the MiddleOn the flip side there are the cities in Iowa. Really can't speak to the irregular growth and what caused it or to why other metros passed Iowa on by. muon has what seems a pretty accurate rundown of the metros and who they employ, though many smaller hubs seem haven't been so lucky (Ft. Dodge, Mason City, Ottumwa, Ft. Madison, Keokuk come to mind). Des Moines and Cedar Rapids-Ia City have been so successful that they've provided stability to small towns in their orbit (Waterloo, Dubuque, and the Quad Cities haven't) thus a Solon or Kalona look and are doing better than say an Oelwein.
There is one industry in Iowa that should be noted because Iowa is the largest producer and most of the production facilities are in rural areas--ethanol. The political and economic ramifications of this are substantial but not the point of this thread at the moment, but think about the electric car for a minute.
Anyway, Iowa as noted has the haves (cities--mainly metro Des Moines and Cedar Rapids-Ia City and the have not rural areas. Once upon a time the rural areas produced waves of kids but now rural Iowa is old, very old like WV old (with the exception of food processing towns with lots of immigrants and their kids. Conversely, city Iowa is young, quite young. If you wanted to know the difference between IA and WV in a nutshell then you'd note that while rural IA and rural WV are old, Kanawha Co, WV, the largest in WV, is old too with 21.2% of the population 65 and older while Polk Co, IA it's only 13.5% that's a big honking difference. Nationally, the % of people 65+ is 16.5% Iowa only has 7 counties below the national avg, but they are Polk, Story, Dallas, Warren, Johnson, Linn, and Woodbury (meatpacking)
Of course, there another difference between growing Iowa and declining Iowa who they vote for and we all know what that difference is.
