My yard is riddled with chipmunk holes this summer. My co-worker just complained about the same thing. Her neighbor is at wit's end.
What's going on?
Just nature taking its course.
Nature engages in a constant balancing act between predators and prey. Right now there's an abundance of small animals for predators such as coyotes, foxes and hawks to eat, but that will change. As the predators feast on the smorgasbord out there, their populations will grow. Eventually that will set up a situation where many predators are competing for food, and they'll thin out the prey population.
Then, with insufficient food for all those predators, their numbers will decline, and the cycle will start all over again.
What can be done about chipmunks?
Unfortunately, there's no silver bullet. Trapping is considered the best method for homeowners, but it's probably a temporary solution at best. Even if you manage to rid your yard of chipmunks, more will probably move in.
Check out Ohio State University's chipmunk fact sheet for more information.