Isla Fisher Dr. Mary Lou Larue (voice)
Jim Carrey Horton (voice)
Joey King Katie (voice)
Seth Rogen Morton (voice)
Jaime Pressly Mrs. Quilligan (voice)
Steve Carell Mayor (voice)
Will Arnett Vlad (voice)
Madison Pettis Additional Voices (voice)
Carol Burnett Kangaroo (voice)
Niecy Nash-Betts Miss Yelp (voice)
Chris Wedge Executive Producer
Ken Daurio Screenplay
Cinco Paul Screenplay
Chris Renaud Storyboard Artist
Jonah Hill Tommy (voice)
Rich Moore Additional Storyboarding
Ariel Winter Additional Voices (voice)
Amy Poehler Sally O'Malley (voice)
Dan Fogler Councilman / Yummo Wickersham (voice)
Selena Gomez Helga (voice)
Karen Disher Who Kid (voice), Storyboard Artist
Madison Davenport Additional Voices (voice)
Jesse McCartney JoJo (voice)
Heather Goldenhersh Who Girl (voice)
Dennis Leonard Supervising Sound Editor
Chris Meledandri Executive Producer
J.G. Quintel Additional Storyboarding
Josh Flitter Rudy (voice)
Jeannine Berger Post Production Supervisor
Danny Mann Additional Voices (voice)
Debi Derryberry Who Mom (voice)
Jeff Siergey Additional Storyboarding
John Powell Original Music Composer
Samantha Droke Hildy / Holly (voice)
Fletcher Sheridan Jojo (singing voice) (uncredited)
Ricardo Curtis Head of Story
Isabella Acres Additional Voices (voice)
Frank Marino Additional Storyboarding
Laraine Newman Glummox Mom (voice)
Bob Bergen Additional Voices (voice)
Tim Nordquist Editor, Wickersham Guard 2 (voice)
Arun Ram-Mohan Lighting Artist
Jess Harnell Another Who (voice)
Joe Pasquale The Dentist (voice)
Bill Farmer Willie Bear (voice)
Mona Marshall Additional Voices (voice)
Dr. Seuss Book
Randy Thom Sound Designer, Supervising Sound Editor
Mickie McGowan Additional Voices (voice)
Cal Brunker Storyboard Artist
Colleen O'Shaughnessey Angela (voice)
Bruce Anderson Producer
Shelby Adamowsky Hedy / Hooly (voice)
Jack Angel Old Time Who (voice)
Teresa Ganzel Additional Voices (voice)
Marshall Efron Wickersham Guard 1 (voice)
Jason Fricchione Joe (voice)
Thomas Cardone Art Direction
Jan Rabson Town Cryer (voice)
Audrey Geisel Executive Producer
David Esneault Lighting Director
Wilbert Plijnaar Additional Storyboarding
Tom Carlson Supervising Music Editor
John Cygan Who (voice)
Sherry Lynn Additional Voices (voice)
Kathy Graves Toon Additional Voice (voice)
Rafael Zentil Storyboard Artist
Edmund Fong Additional Storyboarding
Jimmy Hayward Director, Obnoxious Who (voice)
Chris Gilligan Additional Storyboarding
Laura Ortiz Jessica (voice)
Crystal Chesney Additional Storyboarding