It was constructed in 1992 at the site of the lord's west residence, to commemorate the 100th anniversary of the establishment of the Himeji municipality. In 2017, Koko-en signed a sister garden agreement  with Ro Ho En, the Japanese Friendship Garden, in its sister city, Phoenix, Arizona.
- "Japanese Gardens". Official Tourism Guide for Japan Travel. Archived from the original on 2009-02-24. Retrieved 2015-06-15. CS1 maint: discouraged parameter (link)
- "Newspaper article, translation, sister garden". Ro Ho En Board of Directors. Retrieved 2017-06-22. CS1 maint: discouraged parameter (link)
- "Kokoen Garden, Traditional Japanese Garden in Himeji City". EOK. Retrieved 2010-07-04. CS1 maint: discouraged parameter (link)
Media related to Kōko-en at Wikimedia Commons