While other characters simply call him Perry, Dr. Doofenshmirtz always refers to Perry by his full name (Perry the Platypus). He doesn't abbreviate the names of his other nemeses either (Peter the Panda, Planty the Potted Plant, etc.).
The show takes place in Danville, which is in Jefferson County which is in the Tri-State Area. Danville is named after creator Dan Povenmire and Jefferson County is named after co-creator Jeff 'Swampy' Marsh.