Maasim is a first class municipality in the province of Sarangani, Mindanao, Philippines. According to the 2015 census, it has a population of 59,468 people. It is bordered on the west by the municipality of Kiamba, on the easy by Sarangani Bay, on the north by South Cotabato, and on the south by the Celebes Sea. Among the wilds in its rainforest and mountainous areas lives the Philippine tarsier. ^ Census of Population. "Region XII ".