Kaslinsky District is an administrative and municipal district (raion), one of the twenty-seven in Chelyabinsk Oblast, Russia. It is located in the north of the oblast. The area of the district is 3,356 square kilometers (1,296 sq mi). Its administrative center is the town of Kasli. Population : 17,680 (2010 Census); 14,955 ; 30,627 (1989 Soviet census).