Cornelis "Cees" Vervoorn (born 11 April 1960) is a retired swimmer from the Netherlands. He competed at the 1976, 1980 and 1984 Summer Olympics in seven events; in 1980, he finished fourth, sixth and seventh in the 100 m and 200 m butterfly and 4 × 100 m medley relay, respectively. In the 100 m butterfly final, he clocked 55.25, missing the bronze medal by 0.12 s. In the semifinal he swam 55.02, qualifying first for the final. He won a national title in the 100 m freestyle in 1978 and between 1977 and 1984 set more than 30 national records in various butterfly and freestyle events.