Jacobus "Co" Westerik (The Hague, 1924 – Rotterdam, 2018) was a Dutch visual artist, working as a painter and draughtsman over much of the twentieth century. He trained at the Royal Academy of Art in The Hague from 1942 to 1947, and after graduating he travelled to the United States in 1948. On his return to the Netherlands he settled in The Hague as an independent artist.
In 1951 he co-founded the Verve group with Herman Berserik, Jan van Heel, Willem Hussem and Jaap Nanninga; the group dissolved in 1957. During the 1950s and 1960s he combined his practice with teaching at several schools in The Hague and at Ateliers '63 in Haarlem. In 1971 he moved to Rotterdam and kept a studio in the south of France, where he worked alternately until 2010.
Westerik received the Jacob Maris Prize three times, twice for painting and once for drawing, along with other honours such as the Rembrandt Prize of Leiden and the State Prize for Visual Arts and Architecture. In 1999 he was appointed Knight of the Order of the Netherlands Lion, and in 2005 he became an honorary member of Pulchri Studio.