Look for a Form 1099-R that should be provided to you from your 401k custodian--probably next January. TurboTax should make the entry for the 1099-R fairly straight forward. The 1099-R will provide data for the amount that you withdrew and the amount of taxes that were withheld. Enter all requested values from the 1099-R in accordance with the prompts. TurboTax will complete the required entries on appropriate forms. Your distribution from your 401k will be considered as income. It will be taxable at the federal level, and it is most often taxable by your state also. If you were under age 59-1/2 at the time of distribution, then your 1099-R will likely show a Distribution Code of 1. If that is the case, then a 10% penalty will be added to your taxes. The 401k plans have only a few exceptions to waive the penalty.
https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-tax-on-early-distri...
