Johanns confirmed the death Sunday before he was taken by military helicopter to tour the town of Hallam, where every home was damaged or destroyed, vehicles were flipped and splintered trees lay in the streets.
"I've never seen anything like this," Johanns said. "I've been in public office a lot of years, but I've never seen anything like this."
Officials did not release details about the death, but Johanns said there were no other reports of serious injuries.
Saturday's tornadoes capped two days of severe weather that knocked out power to hundred of thousands of people in Nebraska, Iowa, West Virginia, Michigan, Ohio and Pennsylvania. Michigan authorities blamed three deaths on the storm — all due to trees falling on cars Friday.
Residents of Hallam, a town of 276 people, were evacuated 25 miles north to Lincoln overnight. By Sunday morning, the Nebraska National Guard had surrounded Hallam to keep people from entering. That move, authorities said, was a safety precaution as power lines and leaking propane tanks littered the area.
Pat O'Brien, a commander with the Volunteer Hallam Rescue team, said Sunday it was unclear whether more than one tornado hit Hallam.
"If it was one tornado, it was a pretty big one," O'Brien said.
Some areas reported four to six inches of rain and widespread flash flooding. Authorities closed parts of U.S. Highway 77 and state Highway 41, said Nebraska State Patrol spokeswoman Deb Collins.
Heavy damage from high winds and hail was reported in several southern Nebraska counties, including towns of Firth, Wilbur and Beatrice, where several homes were destroyed.
Johanns' state of emergency declaration makes available National Guard troops, the governor's emergency fund and potential federal resources.