I live in IL and contribute to 529 for my 14 year old son. TurboTax is not populating an option for me to enter my contributions. Am I missing something?

You will enter that on the Illinois state return.   When you prepare the state taxes, you will come to a screen that says  Here's the income that Illinois taxes differently.  

Expand the Education section, and then choose either one of the first two option (contributions).   The 2 options are:

College Savings and Prepaid Tuition - If you added money to a college savings pool or pre-paid tuition program, this applies to you. This includes Bright Start and Bright Directions college savings pools and College Illinois pre-paid tuition programs.   If you added money to any of these programs, we'll walk you through the steps to lower your taxable income (so you owe less).

Illinois ABLE - With Illinois ABLE, you can save for qualified disability expenses. The earnings on your investments are federally tax-deferred and tax-free, if used for qualified disability expense.   If you added money to an Illinois ABLE program, this applies to you.   If you added money to this program, we'll walk you through the steps to lower your taxable income (so you owe less).

Illinois 529 contributions - You are allowed to subtract up to $10,000 in contributions if you are single and $20,000 if you are married filing a joint return for contributions you made to the “Bright Start” program, the "College Illinois" Illinois Prepaid Tuition Trust Fund, or the "Bright Directions" program during the tax year. 

The total subtraction for contributions made to both college savings plans may not exceed $10,000 for single filers and $20,000 for joint filers, even if you contributed more. Contributions to any other IRC Section 529 programs may not be deducted.