What we know
The first Castle Rock PO (1871) sat at the Douglas site three miles south; New Memphis's office took the name May 18, 1874; plat filed April 25, 1874.
Today: Town of Castle Rock
Where it was
USGS GNIS Populated Place 169449
The U.S. Geological Survey's official point for this place name.
Sources
Sources are named in the text above. Numbers such as S-0080 refer to our source list. Most newspaper quotations were read in the Colorado Historic Newspapers Collection. Long quotations from recent books are shortened here.