Lauderdale County Sheriff Billy Sollie confirmed the deaths and injuries in an interview.
"He went through the entire plant, shooting individuals through the facility. There was no one small area," Sollie said.
Sollie didn't release the name of the gunman but said he was a Lockheed Martin employee. He had no information on whether the man had been in trouble with his bosses.
Officials at the plant declined to comment and a Lockheed Martin national spokeswoman was unavailable to immediately provide details.
We're just trying to gather information and are working with state and local authorities to determine the details of the incident," said spokeswoman Meaghan Mariman from the company's Bethesda, Md., headquarters.
The Meridian plant builds parts for the C-130J Hercules and vertical stabilizers for F-22 Raptor jets, which are assembled at the plant in Marietta, Ga., along with military transport planes.
Lockheed Martin is the largest defense contractor in the United States. The corporation had sales of $24 billion in 2001. It employs about 125,000 people.
Subsidiary Lockheed Martin Aeronautics Co. is based in Fort Worth, Texas.