A Clinton aide tells ABC News, she left Sunday afternoon from her home in Chappaqua, New York right around the time of her announcement.
She tweeted her first photo from the journey Sunday night:
Clinton hinted at the road trip in the announcement video she released earlier in the day, saying: "I’m hitting the road to earn your vote because it’s your time. And I hope you’ll join me on this journey."
Clinton has nicknamed her van "Scooby," according to a Clinton campaign aide -- a nod to the "Scooby-Doo" cartoon car called "The Mystery Machine."
According to the Clinton campaign, the next six to eight weeks will be a "ramp up" period. She plans to travel across the country, spending time "engaging directly with voters." The campaign said that she will hold a major kick-off rally sometime in May.
She is expected to arrive in Iowa on Monday evening.
ABC's Michael Falcone contributed reporting.