Where do I report my contributions to IA529? It's supposed to be "line 24" on the form, but TT is not prompting me in the State Tax section (or Fed for that matter).

Never mind, I found it.

529 Contributions are not deductible in your Federal return, so you are correct that you aren't asked about that.

TurboTax will prompt you to enter your 529 Plan contributions when you are in your Iowa state tax return:

• On the page with "Do You Have Any Personal Adjustments?" click Yes 
• On the next page, with "Enter Your Personal Adjustments to Income", scroll down to "College Savings Iowa".
• Enter your 529 Plan contributions