The country earned a score of 5.984 out of possible 10, less than 5.987 scored by 46th-ranked Japan. Singapore came in 24th, Thailand 34th and Taiwan 38th.
In 2013, South Korea placed 41st, becoming the highest-ranked East Asian country rooted in the Confucian tradition, ahead of both Japan and Taiwan.
The 2015 report had mainland China listed as the 84th happiest place to live in among the countries surveyed.
North Korea was not included in the survey.
Switzerland topped the 2015 list with a score of 7.587, followed by Iceland (7.561), Denmark (7.527), Norway (7.522) and Canada (7.427). Also included in the top 10 were Finland, the Netherlands, Sweden, New Zealand and Australia.
The United States placed 15th with 7.119, behind Israel (11th, 7.278), Costa Rica (12th, 7.226) and Mexico (14th, 7.187)
The 10 least happy countries were Afghanistan, war-torn Syria and eight nations in sub-Saharan Africa — Togo, Burundi, Benin, Rwanda, Burkina Faso, Ivory Coast, Guinea and Chad.