Coolidge is a city in Pinal County, Arizona, United States. According to the 2010 census, the population of the city is 11,825.Coolidge is home of the Casa Grande Ruins National Monument. The monument was the first historic site to receive protected status by the United States Government in 1892. The ancient city was built about 1200 AD. by the Hohokam people.Coolidge is home to Central Arizona College.