Ron Whitten is correct that Robert White is the architect of Water Gap Country Club, but has it backwards. The course opened in 1926 as Wolf Hollow Country Club, and is now called Water Gap CC. I'm not sure what year they changed the name, but the course used to host an event called the "Eastern Open", with Hagen and crew playing.
From their website;
The layout [Map of 18-hole Course] originally was famed as Wolf Hollow Country Club, birthplace of the Eastern Open and host of a half dozen other major tournaments. The course today is the same well-groomed test that confronted the golfing greats of the Golden Era of Sports. Golfers now tread in the footsteps of such immortals as Walter Hagen, Johnny Farrell, Gene Sarazen, MacDonald Smith, Willie MacFarland, and Leo Diegel.
Having played several other Robert White courses (Skytop, Berkleigh, East Potomac, Glen Brook, Green Hills, Mount Pocono, Pine Lakes, Wiscasset), I have no doubt that he did Water Gap CC and not Tillinghast.