I didn't know I had a 401k until I got it in the mail. If I left did they give the money back or what happens?

You can leave your money in the 401(k) when you quit or change jobs.

 

You can roll it over to another plan or you can withdraw from your 401(k), but there may be an early withdrawal penalty, and you will have to pay taxes on the full amount.

 

Click on the link for more information

 

401 K plan

If you got a check you had 60 days to put that in an IRA, if you choose to do so.