Cave in Rock. Hardin. Village (1901) twenty-five miles southeast of Harrisburg. Named from the natural cave in the bluff along the Ohio River, a landmark for boatmen since the seventeenth century. The name was recorded in a French account of about 1729 as Caverne dans Le Roc. Cave in Rock has been an Illinois state park since 1929 (Hansen, ed., Illinois, 445—46). Post office established March 13, 1832, as Rock and Cave; changed to Cave-in-Rock Oct. 24, 1849.
From Place Names of Illinois by Edward Callary