The State reported that Sanford arrived Wednesday morning at Atlanta's international airport on a flight from Buenos Aires.
Sanford's spokesman Joel Sawyer declined to comment Wednesday morning to The Associated Press. The governor did not return cell phone messages seeking comment.
Sanford planned a news conference at 2 p.m. today at his office in Columbia.
Critics slammed his administration for lying to the public.
"Lies. Lies. Lies. That's all we get from his staff. That's all we get from his people. That's all we get from him," said state Sen. Jake Knotts, R-West Columbia. "Why all the big cover-up?"
The Republican governor told the South Carolina newspaper that he decided at the last minute to go to the South American country. The governor says he had considered hiking on the Appalachian Trail but wanted to do something "exotic."
Sanford was last seen at work Thursday. On Monday, a state legislator raised questions about where he was after hearing reports from security officials that the governor could not be contacted and his whereabouts were unknown. The governor's wife, Jenny Sanford, told The Associated Press she had not seen him since Thursday but was not concerned because he'd told her he wanted to get away and do some writing.
Late Monday, Sanford's staff said he was hiking the Appalachian Trail. They said Tuesday that he had called in and planned to cut his trip short and return to work Wednesday because of all the attention his absence was getting.
The governor's spokesman, Joel Sawyer, said Sanford wanted to get away to clear his head after the legislative session, during which he lost a key battle. Jenny Sanford said Tuesday, "Leave us to our privacy."
Sanford told The State he was alone on the trip to Argentina. He declined to give any additional details about what he did other than to say he drove along the coastline.
Trying to make such a drive could frustrate a weekend visitor to Argentina. In Buenos Aires, the Avenida Costanera is the only coastal road, and it's less than two miles long. Reaching coastal resorts to the south requires a drive of nearly four hours on an inland highway with views of endless cattle ranches. To the north is a river delta of islands reached only by boat.
A spokesman for Argentina's immigration agency wouldn't comment Wednesday on whether Sanford entered the country, citing privacy laws.
When The State asked Sanford at the airport why his staff said he was on the Appalachian Trail, Sanford replied, "I don't know."
Sanford later said "in fairness to his staff," he had told them he might go hiking on the Appalachian Trial.
Lt. Gov. Andre Bauer said he was concerned that the governor's staff lied about Sanford's whereabouts, adding that if they didn't know where he was they should have said so.
"For his staff to lie to the people of South Carolina and say he was one place when in fact he wasn't, that concerns me," Bauer said.
Sanford has been a fan of Argentina for years. While in Congress and since he's said that nation's Social Security system has a model the U.S. should follow.
Sanford, a trim, 49-year-old former real estate investor and Air Force reservist, is typically drained at the end of a legislative session, former aides said. State Sen. Tom Davis, a Beaufort Republican and Sanford's former chief of staff, said he visited with Sanford last Wednesday and could tell the governor was ready for a break.
"It's not unusual to take off and kind of be by himself," Davis said. "It's part of what makes him him."
The governor has long been known as a loner bucking GOP leadership during three U.S. House terms and casting the only dissenting vote on Medicaid coverage for some breast and cervical cancer treatment. He clashes often with the Republicans who control both chambers of his state Legislature, once famously carrying two piglets to the door of the House in opposition to what he said was pork-barrel spending.
But past vacations never left Sanford completely out of touch, said Chris Drummond, Sanford's former spokesman. At worst, Sanford would call in daily or would respond to voice mails.
Who was in charge became the political and practical question.
Essentially, Sanford's staffers said they'd decide who to call if an emergency popped up and the governor couldn't be reached. The state's constitution says a temporary absence would give the lieutenant governor full authority in the state. But the temporary absence has never been defined.
Senate President Pro Tem Glenn McConnell, a Charleston Republican, said the state's law needs to be clarified. He said state residents want important decisions to be made by elected leaders.
"In an emergency," he said, "it should be those people who consult with staff to make a decision and not the other way around."