Original: The peninsula comprises the Mexican states of Yucatán , Campeche , and Quintana Roo ; the northern part of the nation of Belize ; and Guatemala 's northern department of El Petén .
Simplified: The peninsula is covers up the Mexican states of Yucatán , Campeche , and Quintana Roo ; the northern part of Belize ; and Guatemalas northern department of El Petén .