Potatoes last year (also in central Iowa) were not as big or plentiful as the year before which was an exceptional year. I would say last year was an average yield.
I do like growing some potatoes in 5 gallon buckets. Easiest harvest ever. I have five 1.25" diameter holes in the bottom of the bucket that I trim a paper sack or pizza cardboard to fit at the bottom, then I fill the bucket 1/3 full with compost and potting soil mix. I plant the seed potato, bury the pail in the garden to that fill line. Then I add dried grass clippings with a bit of compost or potting soil as the plants grow. This has always worked great.
"Planting" the pails in the ground keeps them from tipping over in the wind (inevidable in this state} and reduces the need to water as the paper breaks down and moisture is either drawn up, or because the sun doesn't bake the moisture out as fast.