All Cast

Jim Carrey

Jim Carrey

Horton (voice)

Steve Carell

Steve Carell

Mayor (voice)

Carol Burnett

Carol Burnett

Kangaroo (voice)

Will Arnett

Will Arnett

Vlad (voice)

Seth Rogen

Seth Rogen

Morton (voice)

Dan Fogler

Dan Fogler

Councilman / Yummo Wickersham (voice)

Isla Fisher

Isla Fisher

Dr. Mary Lou Larue (voice)

Jonah Hill

Jonah Hill

Tommy (voice)

Amy Poehler

Amy Poehler

Sally O'Malley (voice)

Jaime Pressly

Jaime Pressly

Mrs. Quilligan (voice)

Charles Osgood

Charles Osgood

Narrator (voice)

Josh Flitter

Josh Flitter

Rudy (voice)

Niecy Nash-Betts

Niecy Nash-Betts

Miss Yelp (voice)

Jesse McCartney

Jesse McCartney

JoJo (voice)

Shelby Adamowsky

Shelby Adamowsky

Hedy / Hooly (voice)

Jack Angel

Jack Angel

Old Time Who (voice)

Caitlin Rose Anderson

Caitlin Rose Anderson

Helen (voice)

Emily Anderson

Emily Anderson

Heather (voice)

Jan Rabson

Jan Rabson

Town Cryer (voice)

John Cygan

John Cygan

Who (voice)

Jess Harnell

Jess Harnell

Another Who (voice)

Debi Derryberry

Debi Derryberry

Who Mom (voice)

Samantha Droke

Samantha Droke

Hildy / Holly (voice)

Karen Disher

Karen Disher

Who Kid (voice)

Marshall Efron

Marshall Efron

Wickersham Guard 1 (voice)

Bill Farmer

Bill Farmer

Willie Bear (voice)

Jason Fricchione

Jason Fricchione

Joe (voice)

Heather Goldenhersh

Heather Goldenhersh

Who Girl (voice)

Selena Gomez

Selena Gomez

Helga (voice)

Jimmy Hayward

Jimmy Hayward

Obnoxious Who (voice)

Joey King

Joey King

Katie (voice)

Christina Martino

Christina Martino

Heidi / Haley (voice)

Ellie Martino

Ellie Martino

Hanna (voice)

Laraine Newman

Laraine Newman

Glummox Mom (voice)

Tim Nordquist

Tim Nordquist

Wickersham Guard 2 (voice)

Colleen O'Shaughnessey

Colleen O'Shaughnessey

Angela (voice)

Laura Ortiz

Laura Ortiz

Jessica (voice)

Joe Pasquale

Joe Pasquale

The Dentist (voice)

Connor Anderson

Connor Anderson

Who Child #1 (voice)

Isabella Acres

Isabella Acres

Additional Voices (voice)

Bob Bergen

Bob Bergen

Additional Voices (voice)

Jeff Biancalana

Jeff Biancalana

Additional Voices (voice)

Madison Davenport

Madison Davenport

Additional Voices (voice)

Teresa Ganzel

Teresa Ganzel

Additional Voices (voice)

Kathy Graves Toon

Kathy Graves Toon

Additional Voice (voice)

Sherry Lynn

Sherry Lynn

Additional Voices (voice)

Danny Mann

Danny Mann

Additional Voices (voice)

Mona Marshall

Mona Marshall

Additional Voices (voice)

Mickie McGowan

Mickie McGowan

Additional Voices (voice)

Madison Pettis

Madison Pettis

Additional Voices (voice)

Grace Rolek

Grace Rolek

Additional Voices (voice)

Jennessa Rose

Jennessa Rose

Additional Voices (voice)

Ariel Winter

Ariel Winter

Additional Voices (voice)

Fletcher Sheridan

Fletcher Sheridan

Jojo (singing voice) (uncredited)