Sagae is a city located in Yamagata Prefecture, Japan. As of 1 January 2020, the city had an estimated population of 40,131, and a populatio…Sagae is a city located in Yamagata Prefecture, Japan. As of 1 January 2020, the city had an estimated population of 40,131, and a population density of 289 persons per km². The total area of the city is 139.03 square kilometres.