Bill Farmer character Willie Bear / Additional Voices (voice)
Steve Carell character The Mayor of Whoville (voice)
Jim Carrey character Horton (voice)
Carol Burnett character Kangaroo (voice)
Will Arnett character Vlad (voice)
Seth Rogen character Morton (voice)
Isla Fisher character Dr. Mary Lou Larue (voice)
Jonah Hill character Tommy (voice)
Dan Fogler character Councilman / Yummo Wickersham (voice)
Amy Poehler character Sally O'Malley (voice)
Jaime Pressly character Mrs. Quilligan (voice)
Charles Osgood character Narrator (voice)
Josh Flitter character Rudy (voice)
Ariel Winter character Additional Voices (voice)
Niecy Nash character Miss Yelp (voice)
Jesse McCartney character JoJo (voice)
Shelby Adamowsky character Hedy / Hooly / Additional Voices (voice)
Jack Angel character Old Time Who / Additional Voices (voice)
Caitlin Rose Anderson character Helen (voice)
Emily Anderson character Heather (voice)
Jan Rabson character Town Cryer / Additional Voices (voice)
John Cygan character Who / Additional Voices (voice)
Jess Harnell character Another Who / Additional Voices (voice)
Debi Derryberry character Who Mom / Additional Voices (voice)
Samantha Droke character Hildy / Holly (voice)
Karen Disher character Who Kid (voice)
Marshall Efron character Wickersham Guard 1 (voice)
Jason Fricchione character Joe (voice)
Heather Goldenhersh character Who Girl / Additional Voices (voice)
Selena Gomez character Helga (voice)
Jimmy Hayward character Obnoxious Who (voice)
Joey King character Katie (voice)
Christina Martino character Heidi / Haley (voice)
Ellie Martino character Hanna / Additional Voices (voice)
Laraine Newman character Glummox Mom / Additional Voices (voice)
Tim Nordquist character Wickersham Guard 2 (voice)
Colleen O'Shaughnessey character Angela / Additional Voices (voice)
Laura Ortiz character Jessica (voice)
Joe Pasquale character The Dentist (voice)
Connor Anderson character Who Child #1 (voice)
Isabella Acres character Additional Voices (voice)
Bob Bergen character Additional Voices (voice)
Jeff Biancalana character Additional Voices (voice)
Madison Davenport character Additional Voices (voice)
Teresa Ganzel character Additional Voices (voice)
Kathy Graves Toon character Additional Voice (voice)
Sherry Lynn character Additional Voices (voice)
Sherry Lynn character Additional Voice (voice)
Danny Mann character Additional Voices (voice)
Mona Marshall character Additional Voices (voice)
Mickie McGowan character Additional Voices (voice)
Madison Pettis character Additional Voices (voice)
Grace Rolek character Additional Voices (voice)
Jennessa Rose character Additional Voices (voice)
