Where can I dispose of oil based paint in cans?

I put in kitty litter into my paint cans and waited a few days until the liquids hardened up.

I have nothing to do with the dump at all, but will answer based on my past experience. Only hardened open paint cans may be dumped into the trash. If it's liquid still, it either needs to go to hazardous disposal day in Nashua etc or you put in the hardener additive and let it harden.