Secretary Clinton said America remained the "greatest force for peace [and] human dignity the world has ever known" thanks to its overseas diplomats.
"Their work is at the heart of what makes America great and good," she said.
Upon witnessing the bodies of Chris Stevens, Glen Doherty, Tyrone Woodes and Sean Smith returned to Maryland, she urged Americans to carry their memory into the future.
"We will wipe away our tears, stiffen our spines and face the future undaunted," she said.
Mrs Clinton said Americans would continue to work "together, helping and protecting one another, just like Sean, Tyrone, Glen and Chris always did."
President Obama has paid tribute to US envoy Chris Stevens "as everything America could want in an ambassador" as his body and three of his Benghazi embassy staff were returned to US soil.
He said Mr Smith, Glen Doherty, Tyrone Woods and Sean Smith were "four patriots who loved their country, chose to serve it and served it well. They knew the danger and they accepted it."
"They lived and embodied the American ideal," he said.
US Secretary of State Hillary Clinton has paid individual tributes to US Ambassador Chris Stevens and three embassy staff members killed in a rocket attack at the US Consulate in Benghazi.
She offered her "most heartfelt condolences and deepest gratitude" to their families as the bodies of Mr Stevens, Sean Smith, Tyrone Woodes and Glen Doherty were returned to US soil.
Clinton began her speech: "Today we bring home four Americans who gave their lives for our country and our values."
President Obama has witnessed the return of the bodies of US Ambassador Chris Stevens and three embassy staff members killed in the attack on the US consulate in Benghazi, Libya.
The four coffins, draped in the stars and stripes, were carried off a plane at the Andrews Air Force Base in Maryland and placed in waiting hearses.
The President is due to make an address at the ceremony.
The White House has today lambasted Mitt Romney's criticism of the Obama administration following the attack on the US Consulate in Benghazi, Libya.
Romney was "factually wrong" in his claim that a statement sent out by the embassy had sympathised with the attackers, a White House spokesman said.
He described the claims from the Republican presidential candidate as an attempt to score political points during the election campaign.
President Obama will today witness the return of the remains of US Ambassador Chris Stevens and three of his embassy staff killed in attack on the consulate in Benghazi, Libya.
The President will go to Andrews Air Force Base for a ceremony and deliver remarks alongside Secretary of State Hillary Clinton.
The White House has today said there was no "actionable intelligence" in advance of Tuesday's assault of the consulate in Libya.
The air space over Benghazi airport has reopened after an earlier security alert, the airport manager confirmed to Reuters.
The air space over Benghazi airport has been closed for security reasons, according to airport manager Taba Mohammed. He would not elaborate on why the decision was made.
Benghazi air space has been closed since for routine security checks. It may be open in one hour.
Ali Aujali, Libyan Ambassador to the United States has offered an apology to the US at a traditional Eid celebration at the State Department.
Addressing host Hillary Clinton he said;
"Please, Madam Secretary, accept our apology and accept our condolence for the loss of the four Americans, innocent people. They lost their lives in the Libyan territory."