Carolina is a city and municipality on the northeastern coastal plain of Puerto Rico, immediately east of San Juan and Trujillo Alto, north of …Carolina is a city and municipality on the northeastern coastal plain of Puerto Rico, immediately east of San Juan and Trujillo Alto, north of Gurabo and Juncos, and west of Canóvanas and Loíza. Part of the San Juan metropolitan area, Carolina is spread over 12 barrios and the downtown area and administrative center of Carolina Pueblo. In the coastal region of the municipality lies the resort and residential district of Isla Verde, where the main international airport of Puerto Rico, the Luis Muñoz Marín International Airport, is located. Carolina is the third most populated municipality in the archipelago and island.