British Museum | Museum of Modern Art | Metropolitan Museum of Art | American Museum of Natural History | Victoria and Albert Museum | Natural History Museum | San Francisco Museum of Modern Art | Honolulu Museum of Art | museum | Whitney Museum of American Art | Museum of Fine Arts, Boston | Los Angeles County Museum of Art | Solomon R. Guggenheim Museum | National Air and Space Museum | Brooklyn Museum | National Baseball Hall of Fame and Museum | Hermitage Museum | National Museum of Racing and Hall of Fame | Museum of Contemporary Art | Field Museum of Natural History | Philadelphia Museum of Art | Imperial War Museum | Smithsonian American Art Museum | National Museum | National Museum of Natural History | Museum of Fine Arts, Houston | Denver Art Museum | Cleveland Museum of Art | Museum of Contemporary Art, Los Angeles | National Maritime Museum |
Monahan has shown his sculptures at various galleries, collections, and museums, including the Los Angeles Museum of Contemporary Art, the Chinese European Art Center in Xiamen, Bureau Stedelijk in Amsterdam, The National Center for Art in St. Petersburg, Russia, the Royal Academy and the Saatchi Gallery in London, and Museum Boijmans Van Beuningen, The Stedelijk Museum and the Fries Museum, all in the Netherlands.