These crossovers are part of the Tommy Westphall Universe. Tommy Westphall was a child on St. Elsewhere who had autism. In the series finale, it was implied that the entire series took place in his imagination.
Westphall does not include film crossovers, but I included them for completeness in some cases.
So far I connected Thomas Holbrook's groups 1, 2, 4, 6, 7, 10, 12, 13, 15, 18, 21, 24, 27, 29 to 34, and 38.
Click the image for a better view. The series are placed closest to their strongest link and as close to chronological as possible.
Arriving in St. Elsewhere and Westphall
Several series crossed into St. Elsewhere episodes while it was running. Those series were M*A*S*H, The White Shadow, The Bob Newhart Show, and Cheers.
Dr. B. J. Hunnicut from M*A*S*H was mentioned by Dr. Mark Craig in Santa Claus Is Dead.
Warren Coolidge from The White Shadow appeared in over twenty episodes of St. Elsewhere.
Elliot Carlin from The Bob Newhart Show appeared in Close Encounters.
Carla Tortelli, Norm Peterson, and Cliff Clavin from Cheers appeared in Cheers.