Earnhardt was sponsored by General Motors, with the familiar Goodwrench symbol painted on his black Chevrolet bearing the No. 3.
The flag flying outside the plant that bears that number flew at half-staff Wednesday.
Earnhardt had visited the plant at least twice in recent years, one time bringing his race car with him.
"We're GM. He's a GM-sponsored driver. A lot of people here just felt he was part of the family," said Dan Aiello, 50, of Martinsburg, a picker at the plant and a NASCAR and Earnhardt fan.
"My garage walls are plastered with his pictures," Aiello said.
"I've heard that more people in GM missed work Monday than the day after Kennedy died," said Jim Zachery, 51, a fork-lift operator who lives in Martinsburg.
Zachery said he talked to Earnhardt during his last visit a couple of years ago.
"We asked him if he was scared when he was out there," Zachery said. Earnhardt replied that he knew his work was dangerous, but he loved it, Zachery said.
"He said 'I'd rather be driving a race car than anything else,'" Zachery said.
"It was just devastating," said Jack Smelser, 51, of Great Cacapon, W.Va. "It's a sad day. It just won't be the same."
"It was just shocking," said Nancy Houck, 58, who operates a forklift.
"A lot of people in the plant are race fans," said Sheila Hamilton, 53, a picker from Shepherdstown, W.Va. "The connection with him driving race cars and him coming here, it was personal. It's just sad the way he died. But it may have been the way he would have wanted."
After he'd been at the plant, a worker sent him a letter. Earnhardt responded by sending tickets to races, Aiello said.
"He was very personable," said Zachery. "He just seemed like the guy next door. He didn't put himself on a pedestal above everybody. He was such a young man, only 49. Now, he's a part of history."