This is a set of useful websites where more resources can be found. 

A. Official Websites

Jeju Studies Archives at the Jeju Institute (Jeju local government-affiliated website) http://www.jst.re.kr/

Jejueo Center at Jeju National University http://malgeul.jejunu.ac.kr/

Tamla Culture Research Institute at Jeju National University  http://tamla.jejunu.ac.kr/

Digital Dictionary for Jeju Culture, The Academy of Korean Studies (Korean central government-affiliated website) http://jeju.grandculture.net/Contents?local=jeju&dataType=0201

The Encyclopedia of Seogwipo (English, Korean central government-affiliated website) 

 http://e-seogwipo.grandculture.net/?local=e-seogwipo

The Encyclopedia of Jeju (Korean, Korean central government-affiliated website)  http://jeju.grandculture.net/?local=jeju

B. Private websites

Jejueo Preservation Society http://www.jejueo.com/main

Jeju Palimpsest (Re-examining the history of Jeju island, English) https://jinmunhak.wordpress.com/