Why did some mid-19th Century Irish-American immigrants settle in Iowa?

I live in Iowa and I have a deep Irish heritage. My great-great-great-great-grandparents, Charles and Margaret Stockdale, left Ireland in 1854 and eventually settled in Iowa. Iowa actually has a substantial Irish population. I was wondering why a few Irish settled in rural, desolate Iowa to farm when they failed as farmers in Ireland during the famine and most of their countrymen settled in the big Northeastern cities.