8,205.91 sq mi ( &&&&&&&&&&021253.&&&&&0 21,253 km 2 ) State map highlighting Saguache County San Juan County 111 Silverton 1876-01-31 Split from Lake County . Named for the San Juan River and San Juan Mountains , which in turn were named for Saint John the Evangelist . &&&&&&&&&&&&0578.&&&&&0 578 &&&&&&&&&&&01007.480000 1,007.48 sq mi ( &&&&&&&&&&&02609.&&&&&0 2,609 km 2 )