Coal Township is a township in Northumberland County, Pennsylvania, United States. The population at the 2020 Census was 10,136, which was a decline from the figure of 10,383 tabulated in 2010. According to the United States Census Bureau, the township has a total area of 26.5 square miles, of which 26.5 square miles is land and 0.04 square mil…Coal Township is a township in Northumberland County, Pennsylvania, United States. The population at the 2020 Census was 10,136, which was a decline from the figure of 10,383 tabulated in 2010. According to the United States Census Bureau, the township has a total area of 26.5 square miles, of which 26.5 square miles is land and 0.04 square miles is water.