 | Jason Ian Drucker als Greg Heffley |
 | Alicia Silverstone als Susan Heffley |
 | Tom Everett Scott als Frank Heffley |
 | Charlie Wright als Rodrick Heffley |
 | Owen Asztalos als Rowley Jefferson |
 | Wyatt Walters als Manny Heffley |
 | Dylan Walters als Manny Heffley |
 | Joshua Hoover als Mac Digby |
 | Chris Coppola als Beardo |
 | Kimberli Lincoln als Mrs. Beardo |
 | Mira Silverman als Brandi Beardo |
 | Carlos Guerrero als Luis |
 | Danny Vinson als Hog Man |
| Stephen 'Big Steve' Dupree als Tall Farmer |
 | Neva Howell als Farmer Lady |
 | Ricky Muse als Butter Vendor |
 | Taylor St. Clair als Carnie |
 | Kurt Yue als Fake Dad |
 | Jacinte Blankenship als Security Guard |
 | Beth Keener als Reporter |
 | Mimi Gould als Meemaw |
 | Emma Wetzel als Country Fair Girl |
 | Elijah Marcano als Corny's Host |
 | Apollo GT als XBox Vendor / DXRacer Player |
| Alma Kent als Teen Bystander |
 | Alexa Blair Robertson als Cute Girl #1 |
 | Courtney Lauren Cummings als Cute Girl #2 |
| Robert Hendren als Motorcycle Cop |
| Sofia Bowers als Pigtails Girl |
| Jody Thompson als Uncle Gerald |
 | Stephen Ruffin als Gamer |
| Anthony Ianitello als Diaper Hands Cosplayer |
| Nathaniel Dickson als Brandon Beardo |
| Jake Sterner als Brent Beardo |
| Bobby Akers als Gaming Expo Attendee (uncredited) |
 | Lariah Alexandria als Corny Kid (uncredited) |
| Madison Alsobrook als Expo Kid (uncredited) |
| Cassidy Balkcom als Corny's Waitress (uncredited) |
| Taylor Barton als Fair Kid (uncredited) |
| Alicia Beshears als Fair Teen (uncredited) |
| Kimberly Blaurock als Professional Cosplayer (uncredited) |
| Joshua Booker als Gaming Expo Attendee (uncredited) |
 | Maiya Boyd als Corny Heeley Kid (uncredited) |
| Michael Bunch als Laughing Corny's Waiter (uncredited) |
| Benton Burnett als Cowboy Family (uncredited) |
| Randy Burnett als Cowboy Family (uncredited) |
 | Jamel Chambers als Expo Gamer Attendee (uncredited) |
| Jeremy Chesser als Corny Patron (uncredited) |
| Kristen Danielle als Expo Gamer (uncredited) |
| Aerielle Dodson als Goth County Fair Patron (uncredited) |
| Olivia Dodson als County Fair Patron in Floral (uncredited) |
| Jacob Evans als Expo Kid (uncredited) |
| Juan Gaspard als Festival Vendor (uncredited) |
| James Gill als Steampunk Giant (uncredited) |
| Ben Hammock als Fair Employee (uncredited) |
| Simone Kiffany Jenkins als Passenger (uncredited) |
| Kenneth Jones als Mechanic (uncredited) |
| Tegan Jones als Party Guest (uncredited) |
| Jay D. Kacho als Man Splashed by the Pool (uncredited) |
 | Jeff Kinney als Man at Player Expo (uncredited) |
| Tylon Larry als Fair Kid (uncredited) |
 | Shane Donovan Lewis als Corny's Kid (uncredited) |
 | John Merical als Driver (uncredited) |
| Davis Pak als Boy (voice) (uncredited) |
| Anthony Vance Pierce als Adult Fairgoer (uncredited) |
| Candy Rachor als Corny Patron (uncredited) |
| Jonathan Rush als Expo Gamer Attendee (uncredited) |
 | Christina Michelle Williams als Corny Parent (uncredited) |
| David Bowers | Director |
| Nina Jacobson | Producer |
| Jeff Kinney | Book |
| Brad Simpson | Producer |
| Anthony B. Richmond | Director of Photography |
| Troy Takaki | Editor |
| David Bowers | Executive Producer |
| Mary Claire Hannan | Costume Design |
| Jeff Kinney | Executive Producer |
| Ed Shearmur | Music |
| Aaron Osborne | Production Design |
| Tasha Clarkson | Set Decoration |
| Heath M. Howard | Associate Producer |
| Erin Cochran | Art Direction |
| Jeff Kinney | Writer |
| Timothy M. Bourne | Executive Producer |
| Courtney Bright | Casting |
| Nicole Daniels | Casting |
| David Bowers | Writer |
| Grady Allen Bishop | Camera Car |
| Grady Allen Bishop | Stunts |
| Melanie Deforrest | Makeup Artist |
| Chris Diamantides | Makeup Artist |
| Jessie Gambardella | Makeup Artist |
| Travis Pates | Makeup Department Head |
| Danny Brown | Assistant Art Director |
| Jonathan Dossman | Set Dresser |
| Jeff Ginn | Assistant Art Director |
| Amber Goodrum | Set Dresser |
| Kristen Jenkins | Set Designer |
| Cara Price | Set Decoration Buyer |
| Jason Vigdor | Set Dresser |
| David Mathew Weeks | Set Dresser |
| Marc Glassman | Sound Designer |
| Wayne Lemmer | Supervising Sound Editor |
| Wayne Lemmer | Sound Re-Recording Mixer |
| Derek Vanderhorst | Supervising Sound Editor |
| Derek Vanderhorst | Sound Re-Recording Mixer |
| Manuela Cripps | Visual Effects Producer |
| Wes Dorough | Visual Effects Producer |
| Robin Scott Graham | Visual Effects Supervisor |
| Chris LeDoux | Visual Effects Supervisor |
| Tim LeDoux | Visual Effects Supervisor |
| Bobo Skipper | Visual Effects Supervisor |
| Sara Cobbeldick | Set Costumer |
| K. Drew Fuller | Costume Supervisor |
| Les Morgan | Set Costumer |
| Reese Spensley | Set Costumer |
| Joulles Wright | Costume Supervisor |
| Korii Young | Set Costumer |
| Tom Brown | Music Arranger |
| Scott Christopher Kelly | Stand In |
| Peter Burgis | Foley Artist |
| Adam Bourne | Foley Editor |
| Jason Swanscott | Foley Artist |
| Renée Tondelli | ADR Editor |
| Glen Gathard | Foley Mixer |
| Zoe Freed | Foley Artist |
| Leay Cangelosi | Hairstylist |
| Moe Coles | Hairstylist |
| Jennifer Hodges | Hairstylist |
| Adruitha Lee | Hair Department Head |
| Linda Traxler | Hairstylist |
| Michealle Vanderpool | Hairstylist |
