In the early 20th century, major changes would come to Montauk. In the mid 1920s, New York’s master builder Robert Moses established state parks at Montauk Point and Hither Hills, and constructed the Montauk Point State Parkway to the Point in 1930-31. Meanwhile, in 1925, entrepreneur Carl Fisher, creator of the city of Miami Beach, bought thousands of Montauk acres to develop a resort for the wealthy, which included miles of roads, houses, polo fields, the Montauk Yacht Club, the Montauk Manor, golf course, and more. Then, after World War II, came a prolific motel-hotel construction boom, and battles over housing developments and acquisition of land for parks that continued through the 1960s and beyond. Through it all, Second House maintained its quiet, historic dignity as progress grew around it.

With the death of Mrs. Kennedy in 1965, the house stood empty for a time. Many repairs were needed to restore this historic home. In 1968 the family arranged to turn the house over to the Town of East Hampton and the New York State Historical Trust. The town reached an agreement in 1969 for the Montauk Historical Society to operate a museum in Second House, which officially opened to the public on June 28, 1969. The Society continues to manage the museum today and has held annual craft fairs there since the early 1970s.

Second House has witnessed the transition of Montauk from its days as a lonely, isolated peninsula where few dared tread, to a summer resort community burgeoning with tourists. It serves as a reminder of a more peaceful time when travelers came to enjoy hiking, fishing, beautiful scenery, or to simply enjoy the fresh air of a small, faraway seacoast town.