cast
- Jim Carrey
- Horton
- Steve Carell
- Mayor
- Carol Burnett
- Kangaroo
- Will Arnett
- Vlad
- Seth Rogen
- Morton
- Dan Fogler
- Councilman/Yummo Wickersham
- Isla Fisher
- Dr. Mary Lou Larue
- Jonah Hill
- Tommy
- Amy Poehler
- Sally O'Malley
- Jaime Pressly
- Mrs. Quilligan
- Charles Osgood
- Narrator
- Josh Flitter
- Rudy
- Niecy Nash
- Miss Yelp
- Jesse McCartney
- JoJo
- Shelby Adamowsky
- Hedy/Hooly
- Jack Angel
- Old Time Who, Additional Voices
- Caitlin Rose Anderson
- Helen
- Emily Anderson
- Heather
- Jan Rabson
- Town Cryer, Additional Voices
- John Cygan
- Who, Additional Voices
- Jess Harnell
- Another Who, Additional Voices
- Debi Derryberry
- Who Mom
- Samantha Droke
- Hildy/Holly
- Karen Disher
- Who Kid
- Marshall Erwin Efron
- Wickersham Guard 1
- Bill Farmer
- Willie Bear
- Jason Fricchione
- Joe
- Heather Goldenhersh
- Who Girl, Additional Voices
- Selena Gomez
- Helga
- James Hayward
- Obnoxious Who
- Joey King
- Katie
- Christina Martino
- Heidi/Haley
- Ellie Martino
- Hanna
- Laraine Newman
- Glummox Mom, Additional Voices
- Tim Nordquist
- Wickersham Guard 2
- Colleen O'Shaughnessey
- Angela, Additional Voices
- Laura Ortiz
- Jessica
- Joe Pasquale
- The Dentist
- Isabella Acres
- Additional Voices
- Mona Marshall
- Additional Voices
- Connor Anderson
- Additional Voices
- Mickie T. McGowan
- Additional Voices
- Bob Bergen
- Additional Voices
- Madison Pettis
- Additional Voices
- Madison Davenport
- Additional Voices
- Teresa Ganzel
- Additional Voices
- Ariel Winter
- Additional Voices
- Sherry Lynn
- Additional Voices
- Elena Martino
- Additional Voices
- Danny Mann
- Additional Voices
crew
- Jimmy Hayward
- Director
- Steve Martino
- Director
- Bob Gordon
- Producer
- Bruce Anderson
- Producer
- Cinco Paul
- Screenwriter
- Dr. Seuss
- Book Author
- Ken Daurio
- Screenwriter
- Theodor Geisel
- Book Author
- John Powell
- Composer (Music Score)
- Audrey Geisel
- Executive Producer
- Chris Wedge
- Executive Producer
- Christopher Meledandri
- Executive Producer
- Randy Thom
- Sound/Sound Designer, Supervising Sound Editor, Re-Recording Mixer
- Antonin Plante
- Animator
- Chip Lotierzo
- Animator
- David "Bloke" Sloss
- Animator
- David S. Pent
- Animator
- Derek Rozmes
- Animator
- Gregory Rizzi
- Animator
- Jackie Fortin
- Animator
- James Campbell
- Animator
- Jason S. Martinsen
- Animator
- Lluis Llobera
- Animator
- Michael C. Walling
- Animator
- Moonsung Lee
- Animator
- Paul Downs
- Animator
- Paul F. Diaz
- Animator
- Pete Paquette
- Animator
- Rich McKain
- Animator
- Robin "Orca" Luera
- Animator
- Robyne Powell
- Animator
- Ryan Denniston
- Animator
- Ryland Davies
- Animator
- Scott Carroll
- Animator
- Scott Farrell
- Animator
- Tom Saville
- Animator
- Wesley Mandell
- Animator
- Zach Torok
- Animator
- Chris DiGiovanni
- Production Manager
- Samantha Berg
- Production Manager
- Shawn Murphy
- Sound Mixer, Recording
- Aaron "Noodles" Walsman
- Technical Director
- Aaron Hartline
- Supervising Animator
- Adam McMahon
- Model Effects
- Andrea Gard
- Foley Editor
- Ari Rubenstein
- Painter (digital)
- Benjamin Kilgore
- Technical Director
- Brendan Condit
- Technical Director
- Brent Wong
- Model Effects
- Brett Hoffman
- Script Supervisor
- Carl Ludwig
- Research & Development
- Casey Dame
- Technical Director
- Chris Campbell
- First Assistant Editor
- Cindy Slattery
- Production Assistant
- Colette Dahanne
- Sound Effects Editor
- Dave LaMattina
- Assistant to the Director
- Dave Strick
- Model Effects
- David Esneault
- Lighting
- David Mei
- Model Effects
- Dennie Thorpe
- Foley Artist
- Dennis Leonard
- Supervising Sound Editor
- Di Peter Nguyen
- Matte Artist
- Doug Letterman
- Research
- Edward Robbins
- Model Effects
- Ellen Heuer
- Foley Artist
- Erik Swanson
- Recording
- Erin Crackel
- Second Assistant Editor
- Frank Clary
- Foley Recordist
- Frank Rinella
- Foley Mixer
- Galen Tan Chu
- Supervising Animator
- Gary Rizzo
- Re-Recording Mixer
- George Doering
- Musical Performer
- Harry Kim
- Musical Performer
- Heather Bradford
- Research
- Hollywood Studio Orchestra
- Musical Performer
- Hugo M. Ayala
- Research
- Ian Etra
- Technical Director
- Ian M. Burkard
- Model Effects
- Inna Agujen
- Technical Director
- Jacqueline Jones
- Production Assistant
- James Bresnahan
- Supervising Animator
- James Gu
- Technical Director
- James McKee Smith
- Additional Music
- James Parente
- Technical Director
- Jana Vance
- Foley Artist
- Jason Davies
- Technical Director
- Jason Sadler
- Character Design
- Jeannine Berger
- Post Production Supervisor
- Jeff Brodsky
- Technical Director
- Jenga Mwendo
- Model Effects
- Jennifer Brola
- Research
- Jennifer Kagel
- Production Coordinator
- Jeremy Paul Bowker
- Foley Editor
- Jim Passon
- Color Timing
- Jitendra Borse
- Research
- John Ashton Thomas
- Additional Music
- John W. Wheeler
- Second Assistant Editor
- Jonathan Null
- ADR Supervisor
- Juan Pablo Chen
- Model Effects
- Justin Bisceglio
- Research
- Kathy Graves
- Second Assistant Editor
- Kelly Martin
- Producer's Assistant
- Kyrsten Mate
- Sound Effects Editor
- Mac Smith
- Sound Effects Editor
- Marco Burbano
- Technical Director
- Mark Edwards
- Technical Director
- Melanie Martini
- Technical Director
- Michael Fisher
- Musical Performer
- Michael Toriello
- Technical Director
- Mona Falvey
- Producer's Assistant
- Motoko Wada
- Model Effects
- Pete Anthony
- Conductor
- Pete Horner
- Sound Effects Editor
- Randy Trader
- Associate Editor
- Rick Baptist
- Musical Performer
- Robert MacKenzie
- Matte Artist
- Ron DeFelice
- Matte Artist
- Ronni Brown
- Foley Artist
- Sabina Suarez
- Model Effects
- Sang Jun Lee
- Character Design
- Scott Wiser
- Foley Recordist
- Sean England
- Foley Mixer
- Sook Yeon Lee
- Model Effects
- Steve Slanec
- ADR Editor
- Sue Fox
- Foley Supervisor
- Tim Lauber
- Recording
- Todd E.J. Hill
- Technical Director
- Tony Jung
- Model Effects
- Victoria Dedvukaj
- Producer's Assistant
- Vincent Di Nguyen
- Matte Artist
- Vinoad Senguttuvan
- Research
- Yu-Li Liao
- Technical Director

