"Rock" is listed with this date in a table of towns.

The evidence

• “Rock, March 8, 1838 Spring Valley, February 2, 1846.”

  1908-brown-rock-county/05-historic-evolution.md, Vol. 1, PDF p. 140 / book p. 125

  Brown, William Fiske, editor. Rock County, Wisconsin: A New History of Its Cities, Villages, Towns, Citizens and Varied Interests, from the Earliest Times, Up to Date. Chicago: C. F. Cooper & Co., 1908. 2 vols. archive.org/details/rockcountywiscon01brow, archive.org/details/rockcountywiscon02brow.

  Grade A: Found on a page of one of our sources