The Office of Personnel Management announced that workers should return to work on their next regularly scheduled work day, noting that is Thursday for most workers. Nationwide, hundreds of thousands of workers have been furloughed since the shutdown began Oct. 1.
The office encouraged agencies to be flexible for a smooth transition by allowing telework and excused absences in some cases.
"We're back from the (hashtag)shutdown!" the Smithsonian Institution declared on Twitter, announcing that its 19 museums would reopen Thursday. The National Zoo was set to reopen Friday.
The returning workers' presence will be felt on the roads and rails in the Washington region, where commutes have been less crowded over the past two weeks. The regional transit agency, Metro, reported a 20 percent drop in ridership when the shutdown began and has said it lost a few hundred thousand dollars each day.
Workers began filing in well before dawn at the U.S. Geological Survey's campus in Reston, about 20 miles outside of Washington.
"Feels kind of strange," said Kathleen Faison of Ashburn, a training specialist at the survey, as she headed into the office. "I kind of wish they would have kept us out until Monday."
Faison said during the first few days of the shutdown, she followed the news closely, anticipating that she could be called back any day. But by week two, "I just kind of fell into my own personal routine," she said.
She said she considered teleworking for the first day or two but eventually decided "I might as well just get back into the swing of things."
Hydrologist Julian Wayland, carrying his lunch in a paper bag, said he wasn't sure how much work had piled up during the shutdown. His primary job is determining the age of groundwater samples.
"We're definitely behind," he said. "I'm glad it's over."
The impasse had shuttered national parks and monuments, and mostly closed down NASA, the Environmental Protection Agency and the Interior Department. Critical functions of government went on as usual, but the closure and potential default weighed on the economy and spooked the financial markets.
Standard & Poor's estimated the shutdown has taken $24 billion out of the economy.