Petco. The largest pet supply companies in the United States are without a doubt PetSmart and Petco Animal Supplies. PetSmart, which is headquartered in Phoenix, Arizona, brings revenue in from brick-and-mortar stores across the U.S., as well as in Canada and Puerto Rico.

Pet stores and puppy mills are often criticized for how they affect puppy costs. These places usually get their puppies from large breeding places, where making money is more important than the puppies' welfare.