Mason County Courthouse, Mason, Texas. Recorded Texas Historic Landmark - 1988 – GeoffreyLong, CC BY-SA 3.0 – Wikimedia Commons Mason County is located in Texas. About 3,953 people live here (as of 2020). Between 2010 and 2020, the population declined from 4,012 to 3,953. The area covers about 2,414.0 square kilometers. The region is divided into 1 Municipalities. The region was founded in 1858. The name originates from Fort Mason (place) Mason County is county in Texas, United States. More information at www.co.mason.tx.us.