Latex Paint - Latex paint can be disposed of as trash if dry. To dry small amounts, remove lid and let the paint air dry in the can. For larger amounts, mix in kitty litter or pour one-inch layers of paint in a cardboard box lined with a plastic bag.
If latex paint is good usable paint: Recolor Paints - 149B Winter Street - Hanover, MA 02370 https://recyclingworksma.com/recycler/recolor-paints/ (small fee may be applied)
Oil-based Paint - Oil-based paint or stain is considered hazardous waste and is not accepted. Signup to attend a Hazardous Waste Day. For more info: https://ssrcoop.info/