Assuming the chipmunk didn’t come in from an open door or as a gift from your cat, begin by checking the sill around your foundation. The sill is where the concrete foundation meets the studs of the walls. Look for openings around the perimeter of your home that are at least ½ inch wide. Be very thorough in your investigation.
If you don’t find anything, you will have to look along the eaves of your home as well (chipmunks can climb). Don’t forget to check the gaps around pipes, dryer vents, etc. that enter your home, and along the bases and corners of doorways.
Once you find the opening(s), seal it temporarily with newspaper to determine if it is still active. Never permanently seal off a hole unless you are absolutely positive it is no longer being used by an animal. Failure to heed this advice will trap the animal(s) inside your home and can be very costly.
Resources: (online)
Chipmunks
