United States. Bureau of the Census. P.L. 94-171 County Block Map (2010 Census): Clay County, Inset A01, map, January 12, 2011; (https://texashistory.unt.edu/ark:/67531/metapth384618/m1/1/: accessed November 20, 2018), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .