A double open house will be held at the Little Red Schoolhouse, 297 Locust Ave., Cortlandt, and next door at Old St. Peter's Church. At 3 p.m. in the church the historical society will hold its annual memorial service for eight French soldiers who died in the area during the Revolutionary War. During the afternoon the society will dedicate a tree in memory of longtime treasurer, friend and benefactor Edith Ryan Young.