According to the Iowa instructions:
An Iowa resident is an individual that maintains a permanent place of abode in Iowa or is domiciled in Iowa for 183 days or more.
A Nonresident of Iowa is an individual that is not domiciled in Iowa and is a resident of another state.
A Part-Year Resident is an individual that moved into or out of Iowa during the year.
If one spouse is a resident and the other is not and a joint federal return was filed, you may choose to file separate state returns. To file separate returns within your account, you can file the federal return and wait for the return to be accepted. Then, change the filing status for the primary taxpayer and file a separate return for the first spouse. The second spouse will need to create a new account and file the separate state return in that account (if required to file).
For more information, see: