Tom,
You mentioned that, "I would have assumed that a lot of architects dropped out before their time because of the Depression. Surely Tillinghast falls into that category..."
I don't know what bearing this may have on your thinking, but consider what Tilly wrote to Donald Ross less than a year before he died in 1941:
"I was brought here last April and we have been living with the family of my eldest daughter ever since, while recovery has been slow and I am still confined to my room. As against my old normal weight of around 185 I just manage to move the scale beam at 134. However, while recovery has been discouragingly slow, absolute rest is restoring me, but that is what is in store for me from now on – quiet and rest. It’s hard enough to give it all up – that is the golf. When I will be east again is a matter of conjecture. Before the bad weather settled on us, my daughter used to drive me around the country quite a bit. Quite a few golf courses but as far as I was able to observe, only one good one, old Inverness, which is much the same as ever. And it is good to find something in the game that suggests the good old days. So much has changed to the new tempo as to be a bit startling, even to the playing of the game…"
The Depression certainly brought a tremendous slowing down to Tilly's design activities, but look at some of what he was able to do from 1929 till 1935:
Metropolis CC (R&A)
Ridgewood CC (27 holes) (OD)
Inverness Club (R)
Saxon Woods (OD)
Aldecress CC (Alpine) (OD)
Wykagyl CC (R&A)
Gus Wortham GC (FKA Houston CC) (R)
Bethpage State Park, Green course (R), Blue, Red & Black courses (OD)
Swope Memorial GC (OD)
After Tilly finished the PGA Service Tour in August 1937, 25 months that was an extremely concentrated time of golf architectural work, he went into partnership with Billy Bell. They didn't get much work, but together they even went up into Washington state where they are supposed to have done a new original design together. I haven't been able to find out anything about it other than Tilly's mentioning it briefly in a Pacific Coast Golfer article. That same year, 1939, Tilly drove across the country to do his last work on the east coast at the CC of Fairfield. Just 8 months after that he suffered the massive heart attack that left him a shell of a man yet before he died less than two years later, still, as wrote to Ross above, he had his daughter drive him all over the countryside in Ohio so that he could simply look at golf courses through his car window.
I don't think Tilly ever left off being an architect, even when dying...