John Chapman "Chap" Petersen is an American politician, who represented Virginia's 37th House of Delegates district from 2002 to 2006 and the state's 34th Senate district, made up of the city of Fairfax and large parts of Fairfax County, from 2008 to 2024. He placed third in the 2005 Democratic Primary for Virginia Lieutenant Governor and entered the Virginia Senate after successfully challenging Republican incumbent Jeannemarie Devolites Davis in 2007. In 2023, the Virginia Senate's district lines were redrawn, moving Petersen from the 34th district into the 37th district. Petersen lost the Democratic primary for the 37th district that year to Saddam Azlan Salim.