| The show takes place from 1944 to 2002 and follows the lives of three families: the Crawfords, who seek to cover up the Roswell crash and the existence of aliens; the Keys, who are subject to frequent experimentation by the aliens; and the Clarkes, who sheltered one of the surviving aliens from the crash. |
| Name | Character | Episodes |
|---|---|---|
| Dakota Fanning | Allie Keys | 10 |
| Desmond Harrington | Jesse Keys | 10 |
| Ian Tracey | Bill Walker | 10 |
| Julie Ann Emery | Amelia Keys | 10 |
| Ryan Hurst | Tom Clarke | 10 |
| Jason Gray-Stanford | Howard Bowen | 10 |
| Max Martini | Colonel Breck | 10 |
| Anton Yelchin | Jacob Clarke (Child) | 10 |
| Eric Close | John | 10 |
| Nathaniel DeVeaux | Dale Watson | 10 |
| Roger Cross | Captain Walker | 10 |
| Willie Garson | Dr. Kreutz | 10 |
| Emily Bergl | Lisa Clarke | 10 |
| Matt Frewer | Dr. Chet Wakeman | 10 |
| Catherine Dent | Sally Clarke | 10 |
| Brian Markinson | Ray Morrison | 10 |
| Chad Donella | Jacob Clarke | 10 |
| Camille Sullivan | Nina Toth | 10 |
| James Kirk | Jesse Keys (Teen) | 10 |
| Tina Holmes | Anne Crawford | 10 |
| Timothy Webber | Dewey Clayton | 10 |
| James McDaniel | General Beers | 10 |
| Joel Gretsch | Owen Crawford | 10 |
| Chad Morgan | Becky Clarke | 10 |
| John Hawkes | Marty Erickson | 10 |
| Adam Kaufman | Charlie Keys | 10 |
| Gabrielle Rose | Dr. Harriet Penzler | 10 |
| Emily Holmes | Julie Crawford | 10 |
| Tobias Mehler | Lt. Williams | 10 |
| Devin Douglas Drewitz | Charlie Keys (Child) | 10 |
| Steve Burton | Russell Keys | 10 |
| Rei Hance | Mary Crawford | 10 |
| Taylor Reid | Lisa Clarke (Child) | 10 |
| Andy Powers | Eric Crawford | 10 |
| Brenda James | Dr. Ellen Greenspan | 10 |
| Jason Gray-Stanford | 3 | |
| Ben Cotton | Denny | 3 |
| Tina Holmes | 3 | |
| John Hawkes | 3 | |
| Steve Burton | 3 | |
| Julie Benz | Kate Keys | 2 |
| Ryan Hurst | 2 | |
| Anton Yelchin | Jacob Clarke | 2 |
| Linda Ko | Cynthia | 2 |
| Willie Garson | 2 | |
| Catherine Dent | 2 | |
| Chad Donella | Jacob Clarke (Adult) | 2 |
| James Kirk | 2 | |
| Tom Heaton | Ben | 2 |
| Peter Bryant | Tech on Monitors | 2 |
| Chad Morgan | 2 | |
| Devin Douglas Drewitz | Young Charlie | 2 |
| Sam Easton | Doofus | 2 |
| Rondel Reynoldson | Dorothy | 2 |
| Eileen Pedde | Nora | 2 |
| Elle Fanning | Allie at 3 yrs | 1 |
| Kevin Durand | 1 | |
| Justin Chatwin | Clauson | 1 |
| Ian Tracey | 1 | |
| Eric Close | 1 | |
| Michael Jeter | Bill Jeffries (voice) (uncredited) | 1 |
| Michael Jeter | Bill Jeffries | 1 |
| Ty Olsson | Superior Fish Tech | 1 |
| Michael Moriarty | 1 | |
| Antonio Cupo | Guitar Player | 1 |
| Kurt Max Runte | Roadblock Soldier | 1 |
| Tim Henry | Used Car Salesman | 1 |
| Chad Faust | 1 | |
| Philip Granger | 1 | |
| Jim Byrnes | 1 | |
| David Paetkau | Buzz | 1 |
| Alessandro Juliani | 1 | |
| Matt Hill | 1 | |
| Enid-Raye Adams | 1 | |
| Andrew Jackson | 1 | |
| Malcolm Stewart | 1 | |
| Alexandra Purvis | Lisa at 13 yrs | 1 |
| John B. Lowe | Dr Findlay | 1 |
| Brent Stait | 1 | |
| Taylor Reid | Young Lisa | 1 |
| Andy Powers | 1 | |
| Ken Camroux-Taylor | Luke Reynolds | 1 |
| Mark Shera | Radio Caller | 1 |
| Byron Lucas | Danny Holding | 1 |
| Joe MacLeod | Docent | 1 |
| Terry David Mulligan | Interviewer | 1 |
| Jonathon Young | 1 | |
| Roger Haskett | Man in Crowd | 1 |
| Brenda James | 1 |