The points of issue
Copyright page shows 1954 only, with no later dates and no list of other Seuss titles on the copyright page (in the true first the title list appears only on the recto of the rear endpaper). First-issue dust jacket is priced 250/250 on the front flap. The first-state rear panel shows Horton's full ear (not cropped by the quotation), a cloud in the upper left, and a five-branch tree in the upper right; later states crop the ear, drop the cloud, and reduce the tree to two branches. Pictorial boards.
Is this the true first?
The US Random House 1954 edition is the true first. Identification rests on the 1954-only copyright page, the 250/250 jacket price, and the first-state 'full ear' rear-panel artwork, since the text plates are unchanged across printings.
Telling it from reprints & book-club editions
Club editions lack the jacket price, may list later Seuss titles, show the cropped-ear later-state rear panel, and have a smaller trim with a blind-stamp; many surviving copies are later printings with no clear first-edition state.
Frequently asked questions
Is my copy of Horton Hears a Who! a first edition?
Look for these first-edition points: Copyright page shows 1954 only, with no later dates and no list of other Seuss titles on the copyright page (in the true first the title list appears only on the recto of the rear endpaper). First-issue dust jacket is priced 250/250 on the front flap. The first-state rear panel shows Horton's full ear (not cropped by the quotation), a cloud in the upper left, and a five-branch tree in the upper right; later states crop the ear, drop the cloud, and reduce the tree to two branches. Pictorial boards.
How do I tell the first printing from a later one?
Check the copyright page for the publisher's first-printing convention and confirm the points above. The US Random House 1954 edition is the true first. Identification rests on the 1954-only copyright page, the 250/250 jacket price, and the first-state 'full ear' rear-panel artwork, since the text plates are unchanged across printings.
Is the book-club edition the same as the first?
Club editions lack the jacket price, may list later Seuss titles, show the cropped-ear later-state rear panel, and have a smaller trim with a blind-stamp; many surviving copies are later printings with no clear first-edition state.
I have a first edition of Horton Hears a Who! — what should I do?
If you're clearing books, New Mexico Literacy Project offers free pickup in Albuquerque, any condition, and makes sure collectible copies aren't lost. To sell, see the author's collecting guide. Either way, nothing valuable ends up in a landfill.