Yŏnsa County is a kun, or county, in North Hamgyong province, North Korea. It was created following the division of Korea, being split off from Musan county in the 1952 reorganization of local government. The land of Yonsa is high and mountainous, with even the low-lying areas more than 500 meters above sea level. The county is traversed by the Hamgyong Mountains and the Paekmu Plateau.