Mark James DeSaulnier ( də-SOH-nee-ay; born March 31, 1952) is an American politician who has served as a U.S. representative from California since 2015. He has represented the 10th congressional district since 2023, although it was previously numbered the 11th district for his first eight years in office. The district includes most of Contra Costa County, a suburban county in the East Bay. He has been a member of the Democratic Party since 2000; before that, he was a Republican. Before serving in the House of Representatives, DeSaulnier was a member of the Concord City Council (1991–94), a Contra Costa County Supervisor (1994–2006), and a member of the California State Legislature, representing the 11th State Assembly district from 2006 to 2008 and the 7th State Senate district from 2008 to 2015.