According to the census estimate for 2013 (link to page with Excel spreadsheet which may not have the state names but is in alphabetical order), Iowa has 3,090,416 people, which is an increase of about 44,000 people and 1.45% from the official 2010 number.
By contrast, Arizona has an estimated population of nearly 6.63 million — an increase of 234,600 people, or 3.67%, from 2010 to 2013.
The month I was born, Iowa had more people than Arizona. That reversed, ever so barely, by the next estimate.
UPDATE: By the middle of the decade, Iowa could be passed by Utah. Utah.