In 1912, George W. Perkins was appointed chairman of the newly formed Commission by governor Roosevelt. He hired Major William A. Welch as assistant engineer, and in 1914 named him chief engineer and general manager. Under Welch's leadership, the Palisades Interstate Park grew from the initial 10,000 acre (40 km²) Bear Mountain State Park to the more than 40,000 acre (162 km²) Harriman State Park. By 1919 nearly a million people a year were coming to the park.
When work started on the Park there were no existing models or precedents for an endeavor of its nature and scope. Welch organized a massive reforestation program, built 23 new lakes, 100 miles (160 km) of scenic drives and 103 children's camps, where 65,000 urban children enjoyed the outdoors each summer. He helped found the Palisades Interstate Park Trail Conference and served as chairman of the Appalachian Trail Conference.
The Palisades park system has been expanded over the years; it now includes 24 parks and eight historic sites, covering over 100,000 acres (405 km²) along more than 20 miles (32 km) of Hudson River shoreline and beyond: the Commission also oversees Minnewaska State Park Preserve. The commission also operates the Palisades Interstate Parkway, built between 1947 and 1958.
The Palisades Interstate Park was designated a National Historic Landmark in 1965. The area included in the landmarking is the Palisades Park in New Jersey, the Palisades Park in New York State, and the Tallman Mountain State Park in New York State.,