"Secretary Kerry has departed Geneva en route to Boston, Massachusetts," US State Department spokesman John Kirby said.
Kerry, 71, a keen cyclist, had been hospitalized in Geneva — where he met his Iranian counterpart Mohammad Javad Zarif a day before Sunday's accident across the border in the French Alps.
He was initially expected to return to the United States Sunday evening, but his flight was postponed, "for observation overnight for purely precautionary measures," the State Department said.
A yellow ambulance helicopter was seen flying from the Geneva hospital where he had received treatment to the nearby airport, where a US military C-17 aircraft stood waiting on the tarmac, an AFP photographer said.
Kirby said the plane was expected to arrive in Boston "later this evening."
As the plane took off, Kerry himself tweeted, in French, his gratitude to those who had helped him in Switzerland and France after his ordeal.
"I am particularly grateful to the police and remarkable medical teams in Geneva and Scionzier," he said, referring to the French
Alpine village where he fell off his bike Sunday morning.
Kerry's orthopaedic surgeon, Dennis Burke, who performed past hip surgery on him, as well as military medical personnel, were onboard with him.
Tour de France hill
The top US diplomat's fall happened after he had just set out on a planned ride of one of the stages of the Tour de France, the steep and winding Col de la Colombière mountain pass, a local source said.
The top US diplomat, who had been holding talks in Switzerland Saturday on the Iran nuclear crisis, broke his right femur in his fall in the idyllic village of Scionzier, near Chamonix.
On Sunday, Kirby said Kerry was "stable and never lost consciousness," and was expected to make a full recovery.
He also described the top US diplomat as being "in great spirits and active", and said he had spoken by phone with President Barack Obama Sunday evening.
Kerry also spoke with French Foreign Minister Laurent Fabius by telephone Monday morning.
The American "had a good voice" and had spoken in French, a source close to Fabius told AFP, adding that Kerry had vowed to "come back to cycle in France."
He has however had to cancel both a trip to Spain and his attendance at an international meeting in Paris on the crisis over the Islamic State group, Kirby said.
Kerry however plans to "remotely" join Tuesday's Paris talks, which are aimed at reviewing the international coalition's strategy against the
jihadists, who have seized swathes of territory in Iraq and Syria.
The State Department said Deputy Secretary of State Antony Blinken will lead the US delegation in Paris.
No stopping Kerry
Few expected the broken leg to keep the globetrotting Secretary of State on the sidelines, however.
White House spokeswoman Jennifer Psaki, who used to work for Kerry at the State department, claimed the accident would not slow him down.
"I would love to see anyone at the hospital try to stop John Kerry from negotiating and working while recovering from breaking his leg," she tweeted Sunday.
Kerry had asked local officials in eastern France's Haute-Savoie to organize the trip in the beautiful Alpine region.
"He had expressed a wish, a few days ago, to complete a stage of the Tour de France passing through the Col de la Colombière," the local source said, pointing out that "the hill is very well-known for its difficulty."
"Because he loves France and cycling, he decided to climb it on his bicycle," he added.
"If John Kerry came here to bike, it wasn't by chance," Scionzier resident Arfaoui Aymen told AFP, adding that the Col de la Colombière was "the best place in Haute-Savoie for biking."