Forgot to surrender my TN visa

Up until the end of last year, I was working in the US under a TN visa, living in Windsor and crossing back and forth every day. At the end of November, I got laid off, but still have my visa in my posession. I have been offered a new position at a different employer, for which I will need a new TN visa. Will it be a problem that I didn't hand in my old visa? Any advice as to what I should do?

You should have surrendered your I-94 to Canada Customs the day you were laid off since this is how essentially CBP determines whether you are an overstay or not. I don't think it would be problematic but just keep it in mind down the road in case you are terminated again.

It's not a big deal, you can just mail it to:

ACS Inc.
1084 South Laurel Rd.
London, Kentucky 40742
USA

with a letter of explanation.

Or else just surrender it at the POE.