Form W-2 (wage statement) Box D is called the Control Number field. It is usually located below or near the Employer's Name and Address, but you may have to look very carefully for it, as it can occasionally be in a different place. Sometimes there is no Box D Control Number at all. Since the W-2 wage statement is issued by many different employers, in many varied formats, there really isn't a single solution that always describes where the Control Number may be found on any specific, individual, W-2.
That said, the Box D Control Number is a code that uniquely identifies your unique W-2 document in your employer's records. This number is assigned by the company's payroll processing software, and is only needed if attempting to electronically import your W-2 into a tax software program (like TurboTax). Please note that not all W-2s (or employers) will necessarily include or support a Box D Control number. Your alternative to importing a W-2 document is to simply input the same information manually.
The actual Control Number itself is not necessary in completing your tax return. In other words, the W-2 Control Number, whatever it is, will never increase or decrease your actual tax refund (or your amount owed) by a single penny.
If you choose to type in your W-2 manually, rather than importing it electronically, then you should not have to enter anything from Box D at all, if you do not want to. In fact, you can simply leave the field blank. The exceptions to that would be if you are attempting to e-file your return and see some sort of W-2 Control Number related error; or if the program insists on a value before allowing you to continue. In those cases, we have a TurboTax FAQ article that can help. Directly below this text is a link to that FAQ page below.