Horton (voice)

Jim Carrey

Acting

Mayor (voice)

Steve Carell

Acting

Kangaroo (voice)

Carol Burnett

Acting

Vlad (voice)

Will Arnett

Acting

Morton (voice)

Seth Rogen

Acting

Councilman / Yummo Wickersham (voice)

Dan Fogler

Acting

Dr. Mary Lou Larue (voice)

Isla Fisher

Acting

Tommy (voice)

Jonah Hill

Acting

Sally O'Malley (voice)

Amy Poehler

Acting

Mrs. Quilligan (voice)

Jaime Pressly

Acting

Narrator (voice)

Charles Osgood

Acting

Rudy (voice)

Josh Flitter

Acting

Miss Yelp (voice)

Niecy Nash-Betts

Acting

JoJo (voice)

Jesse McCartney

Acting

Hedy / Hooly (voice)

Shelby Adamowsky

Acting

Old Time Who (voice)

Jack Angel

Acting

Helen (voice)

Caitlin Rose Anderson

Acting

Heather (voice)

Emily Anderson

Acting

Town Cryer (voice)

Jan Rabson

Acting

Who (voice)

John Cygan

Acting

Another Who (voice)

Jess Harnell

Acting

Who Mom (voice)

Debi Derryberry

Acting

Hildy / Holly (voice)

Samantha Droke

Acting

Who Kid (voice)

Karen Disher

Acting

Wickersham Guard 1 (voice)

Marshall Efron

Acting

Willie Bear (voice)

Bill Farmer

Acting

Joe (voice)

Jason Fricchione

Acting

Who Girl (voice)

Heather Goldenhersh

Acting

Helga (voice)

Selena Gomez

Acting

Obnoxious Who (voice)

Jimmy Hayward

Visual Effects

Katie (voice)

Joey King

Acting

Heidi / Haley (voice)

Christina Martino

Acting

Hanna (voice)

Ellie Martino

Acting

Glummox Mom (voice)

Laraine Newman

Acting

Wickersham Guard 2 (voice)

Tim Nordquist

Editing

Angela (voice)

Colleen O'Shaughnessey

Acting

Jessica (voice)

Laura Ortiz

Acting

The Dentist (voice)

Joe Pasquale

Acting

Who Child #1 (voice)

Connor Anderson

Acting

Additional Voices (voice)

Isabella Acres

Acting

Additional Voices (voice)

Bob Bergen

Acting

Additional Voices (voice)

Jeff Biancalana

Art

Additional Voices (voice)

Madison Davenport

Acting

Additional Voices (voice)

Teresa Ganzel

Acting

Additional Voice (voice)

Kathy Graves Toon

Editing

Additional Voices (voice)

Sherry Lynn

Acting

Additional Voices (voice)

Danny Mann

Acting

Additional Voices (voice)

Mona Marshall

Acting

Additional Voices (voice)

Mickie McGowan

Acting

Additional Voices (voice)

Madison Pettis

Acting

Additional Voices (voice)

Grace Rolek

Acting

Additional Voices (voice)

Jennessa Rose

Acting

Additional Voices (voice)

Ariel Winter

Acting

Jojo (singing voice) (uncredited)

Fletcher Sheridan

Acting