You will need to first determine what type of paint you have.
OIL-BASED paints are considered Hazardous Materials which may harm the environment. These items must be properly disposed of at a Household Hazardous Waste (HHW) facility or event; to find a HHW facility visit the Michigan Department of Environment, Great Lakes, and Energy at www.michigan.gov/egle
LATEX and ACRYLIC paints: Place open cans of latex or acrylic paints outside or in a well-ventilated area to allow the paint to harden. This process can take a couple of days to a few weeks, depending on the temperature and humidity. Once the paint is solid and completely dry - it can be thrown away with your regular trash (leave the lid off of the can).
If there is a lot of pain left in the can you can add kitty litter or an oil absorbent material to dry the pain out more quickly.
Alternatively, apply any leftover paint to scrap lumber or cardboard and allow it to safely dry
Recycle Ann Arbor will accept water-based paints ONLY. 734-971-7400
Watch the website for future Household Hazardous Waste (HHW) collection events.
ERG Environmental 734-437-9650 accepts hazardous materials including oil-based paints, stains, and solvents.