If you have a withdrawal or distribution, you will get a 1099–R. The withdrawal or distribution is taxable even if you did not cash the check. It is taxable because you have received the money and could cash the check at any time even though you have not done so. if you are under age 59 1/2, you are also subject to a 10% early withdrawal penalty.
I don’t know why your plan made a distribution to you but I can guess at one common reason. Sometimes, when an employee leaves a employer and has only a small amount of money in the plan, the maintenance fees that the employer hast to pay to maintain the account of the ex-employee are so high that the employer would rather kick you out of the plan. When this happens, the plan would be required to send you a letter informing you of this situation and informing you of your options. You would have had 60 days to roll over the money into another qualified retirement account, either by opening a qualifying IRA at a private bank or brokerage, or by rolling over the money into the retirement account of your new employer. In this case, the money becomes part of your current retirement funds and is not taxable until you withdraw it in retirement. Since it has obviously been more than 60 days and you did not roll the money over into a new qualified account, then it is treated as a fully taxable distribution.
