There was one in Colorado in 2013: https://ballotpedia.org/%22Whether_to_Pursue_the_Creation_of_a_51st_State%22_Colorado_County_Referendum_Questions_(November_2013) … and Puerto Rico in 2012: https://en.wikipedia.org/wiki/Puerto_Rican_status_referendum,_2012 …https://twitter.com/daveweigel/status/746121044994428928 …
I am a registered Democrat simply to vote in primary elections due to the predominance of Democrats in my area.