This order of battle could not have been constructed without the aid and knowledge of Keith Rowe and Dan Allmacher, who quite literally have the best informed presentation on the ROK's Order of Battle, outside a government.
AsianDefense Group @ Yahoo Groups -- This site has quite a bit of discussion regarding Korea including the writings and documents of Keith Rowe and Dan Allmacher
Korea Insititute of Military History. The Korean War, vol 1. (Lincoln: University of Nebraska; 2000): p. 71, 83
21st Infantry Regiment
The 21st Infantry Regiment was originally activated as the 21st Regiment on February 1, 1949 at Kwangjuand and was first commanded by Lt. Col. Park Ki Byong. The unit was initially to the 5th Division.