If you are in possession of counterfeit money, is that a strict liability thing, or do they have to prove you KNEW it was counterfeit?

Example: Say that I go to the grocery store tomarrow, and pay with a $100 dollar bill. I get a $20 dollar bill back in change. Little do I know, that $20 dollar bill I got back in change is actually a well made counterfeit. Later, I go into a different store and use that counterfeit $20 dollar bill to make... show more Example:

Say that I go to the grocery store tomarrow, and pay with a $100 dollar bill. I get a $20 dollar bill back in change.

Little do I know, that $20 dollar bill I got back in change is actually a well made counterfeit.

Later, I go into a different store and use that counterfeit $20 dollar bill to make another purchase. But this store holds the bill up to the light or marks it with a detector pen, revealing it is counterfeit and they call the police.

Am I automatically guilty of a crime for possessing and passing it?

Or would the fact that I didnt know it was counterfeit and simply got it as change from somewhere be a defense?
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