Cossayuna, NY Is a town located in Washington County. The Cossayuna lake is the largest body of water around in this area. Fishing, boating, hiking and mountain climbing are popular activities to do in this area. There are several cabins that can be rented near the lake, making this a nice spot to enjoy a weekend get-away. The population is about 478 people. The best time to visit is during the summer so you can enjoy the outside recreational activities that this community has to offer. Two of the favorite businesses in the area are the Lakeside Country Store and Cossayuna Lake Improvement Association This city does have a lot of visitors because it is the home of 34 mountain summits and peaks. The best time to visit is during the winter. One of the more popular Mountain Summits is the Dugway Mountain Summit.