Prolific and in great demand, he illustrated for a wide variety of magazines and advertisers, but found time as well to paint many important murals. Notable among them were those for the Los Angeles Public Library, The General Motors mural at the 1939 World's Fair in New York, The Tennessee State Office Building, the Eastern Airlines building in Rockefeller Center, and the Raleigh Room at the Hotel Warwick in New York City.
Dean was president of the Society of Illustrators from 1922-1926 and was selected to its Hall of Fame in 1959. He taught illustration at the Arts Students League in New York, and by example created a "Cornwell School."
