How to enter section 457 distributions where federal and state taxable amounts are different?

This information is addressed in the Federal section of TurboTax. After you enter the information from the Form 1099-R that reports the retirement plan distribution, you'll be prompted to select your state. Once you do this, TurboTax will ask you for additional state-specific information. The details depend on your state. 

Click the screenshots below for examples of how the screens look for Massachusetts. The screens will vary depending on your state, but when you answer the questions during the 1099-R interview TurboTax will automatically calculate the amount of the distribution that is taxable on your state tax return.