Geer illustrated many children’s books and wrote and illustrated two of his own. He also designed numerous book jackets.
Many of the buildings in his illustrations feature Second Empire architecture, with their characteristic Mansard roofs.
The illustrator lived (until his death in 2008) in Maine, where he enjoyed sailing and painting watercolors. Over the years he built several boats.
The Mulford Gallery hosted a retrospective of the works of Charles Geer, through June 15th, 2009. Geer was one of the most respected and prolific illustrators of children's and romantic novels by authors such as Stephan Birmingham, Georgette Heyer, Mary Stewart. He did colorful and imaginative examples of sketches and illustrations for this covers, as well as most exquisite depictions of the coast of Maine and Nova Scotia, where he and his wife, Mary retired and sailed from their home in Rockland.