Justin R. Cronin (October 9, 1980 – November 11, 2020) was an American politician who served as a Republican member of the South Dakota House of Representatives from January 2009 to 2017 and the South Dakota State Senate from 2017 until his resignation in August 2019 due to health reasons. Cronin won his uncontested seat for an additional term in 2016. He died at his home in Pierre, South Dakota at the age of 40.