The state income tax your employer withholds must be reported on your annual W-2. Your employer includes your federal withholding information on the same form. This means your state W-2 is the same document as your federal W-2.
Your employer is supposed to distribute your W-2 by the date mandated by the federal government, generally the last day of January. Your employer can hand you the form or mail it to your address. In the latter case, the W-2 envelope needs to include a postmark showing the form was mailed by the due date.
Your employer's state ID number is listed in box 15 of the W-2. Your wages that were subject to state income tax are reflected in box 16 and the state income tax withheld from those wages are shown in box 17.
Your employer must file your W-2 with the Social Security Administration and the state revenue agency after sending you the form. If the state does not charge an income tax, your W-2 will not show any state information and you do not need to file a state return.
Many states adhere to federal guidelines for tax filing due dates, but a few have different deadlines. Consult with the state revenue agency for the deadline that applies to you. If you cannot file your state return in time and need an extension, contact the state revenue agency for related deadlines.
If you lost your W-2 or never received one, you may be able to request a copy from the state revenue agency, which might charge a fee. You can request a copy of your W-2 for previous tax years from the IRS. Use Form 4506 to make the request. For a fee, the IRS will send you a copy of your entire return, which includes an actual copy of your W-2 that reflects state information. Otherwise, you can request a free transcript from the IRS--this route does not provide state information, only federal data.