Kayaking on Flagstaff lake with Bigelow mountains in back Welcome to Stratton-Eustis! Eustis and Stratton are both in Franklin County. Eustis and Stratton together have a population of about 618 as of the 2010 census. Eustis is located on the High Peaks Scenic Byway and Stratton near the 500-acre Flagstaff Lake