A joint account was closed out before my mother's passing but the check was not cashed out. Who does the cash belong to?

We'll have to wait for an answer. We don't have enough information. When an account is closed, a cashier's check is the norm. If it is written to the deceased AND another person, it can be cashed as soon as there is a death certificate. If it is written to the deceased OR another person, it can be cashed by the other person right away. The same is true if it was written to the person alone. However, if the check was written to the deceased person alone, it will need to go into an estate account. Pretty simple.

Seems you're getting a variety of answers and I'll add one more. You state this is a joint account - if the account has "survivorship rights", once one account holder passes away - the account becomes the property of the remaining account holder. If I'm understanding your question - because the check was not cashed there is still money sitting there and I don't understand how the account can be officially closed - as the money would remain in the account until the check is cashed. Regardless - with your mother gone - in most cases any existing money would belong to the other joint account holder and not be considered a part of the estate. There are accounts - such as one called "tenets in common" that would be an exception. And of course - everything hinges on who the check was written to and how long ago. It's my understanding a check can still be cashed six months after it is written with the exception of some businesses checks which list a specific expiration date.

Once the person dies, the account is frozen. That's to stop people from trying to cash out and avoid probate. Now go see an attorney and do probate properly. Bring the Will and all the bank statements. Forget about the check, it's all probate now.

Jan, the issue is not so much the timing as the nature and purpose of the check, and as Jessie advises, the payee of the check.

What's the purpose of the check? I.e., for what and for whom was it written?

Who is the check written to? If it is written to the deceased, then it belongs to the estate. If it is written to someone else, it belongs to them.