Pocantico Hills is an 18-hole course with 13 greens, including one double green. It reverses on itself on several holes. There are 8 fairways not including the 4 par 3 holes. The course was open for play in 1938, one year after JD Rockefeller, Sr. passed away. His son, JD Rockefeller, Jr. and the five grandsons hired Flynn to build a new course on the family estate to replace the existing outmoded 9-hole course. It is a fine course on perhaps the most magnificent estate in America. Today there are no fairway lines as everything is mowed at the same height, about the height of a typical step cut. The greens have shrunken quite a bit, but it retains its interest and beauty as the course winds about the property and takes the golfer to some magnificent overlooks and through theme gardens, rare specimen trees, sculptures and various views of Mr. Rockefeller, Sr.'s home, Kykuit.
Flynn designed another famous estate course for Albert Lasker in Lake Forest, IL known as Mill Road Farm GC. It was one of the longest and most difficult courses in its day (1926) at 7000 yards and played for some time as a par 70.
Flynn redesigned (1924) the Friendship estate course in Washington, DC for newspaper publisher Edward McLean.
Flynn designed a fascinating 3-green, 9-hole golf course for the estate of Robert Cassatt, nephew of painter Mary Cassatt and President of the Pennsylvania Railroad.
Flynn designed a 9-hole course (1930) for Dr. George Woodward, married to Gertrude Houston, daughter of real estate developer and railroad entrepreneur Henry Houston. Houston and Woodward developed Chestnut Hill outside of Philadelphia, near the Woodward estate. I don't think the course was ever built, perhaps due to the Depression.