Katherine Milhous (November 27, 1894-December 5, 1977) was an American artist, illustrator, and writer. In 1951, her book The Egg Tree (1950) won the Caldecott Medal.
Biography on Wikipedia: https://en.wikipedia.org/wiki/Katherine_Milhous
Pennsylvania Costumes and Handicrafts, the Pennsylvania Germans by Katherine Milhous
c.1936-1941 / Lithographic poster promoting Lancaster County / Library of Congress, DC
Katherine Milhous on Artnet: http://www.artnet.com/artists/katherine-milhous/