I'm happy to announce that the EXTANT ROUNDHOUSE SURVEY that I created years ago has been updated and is joined by a new BYGONE ROUNDHOUSE SURVEY listing an additional 3,347 facilities that once existed in the US.

They are available on the National Railway Historical Society (NRHS) website at [https://nrhs.com/programs/extant-and-bygone-roundhouses/ .
XL, PDF and CSV versions are available and I plan to update these listings 1-2 times per year as required based upon additional information received.