Caribou is the second largest city in Aroostook County, Maine, United States. Its population was 7,396 at the 2020 census. The city is a ser…Caribou is the second largest city in Aroostook County, Maine, United States. Its population was 7,396 at the 2020 census. The city is a service center for the agricultural and tourism industries, and the location of a National Weather Service Forecast Office.