As a Maine resident, Maine will tax all of your income regardless of where you earn it. Therefore, when you enter your W-2 into TurboTax, you first want to treat all of your W-2 copies as if they were one: enter the Maine amount as reported on the W-2 with a box 15 of ME, and then boxes 16 and 17 in their corresponding spots. Next, you will click on "select another" and continue to add the state name from box 15 and the corresponding amounts is boxes 16 and 17. If there are any local taxes withheld, then you will enter these amounts found in boxes 18 and 19, clicking "select another" for each different locality. Box 20 is the locality ID, and then you add the state associated. The screenshot below provides guidance.
What should happen is that the correct taxable amount will transfer to your Maine return. However, you will want to prepare all nonresident returns first, that is the other states where you worked and will be taxed (MA and MO; NH does not have state income tax). This is because on the Maine return, Maine will issue a tax credit for the amount of tax you must pay to each of these states for the amount of income earned in each. This FAQ provides more information: https://ttlc.intuit.com/replies/3302052
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
