Authorities said 50-year-old Ronald Davis walked into McBride Lumber Co. and shot the four individuals. About 16 other employees in the building but were unharmed.
"He knew who he was after. He knew who he was going to see," said Montgomery County Sheriff Dempsey Owens.
After the shooting, Davis went home and shot himself in the head, but he survived. Deputies went to his house and knocked on the door, but no one answered. When a deputy peered through the window, he saw Davis sitting on the couch "with his head hung down."
A handgun and a six-page note were found nearby. Police did not release what the note said.
Both Davis and the surviving co-worker are being treated at hospitals. Their conditions have not been released.
Witnesses described Davis as a disgruntled employee, but it was unclear what he was upset about. And other than failing to validate a deer, police said Davis did not have a criminal history.
The names of the victims have not been released.
McBride Lumber is a family-owned business that makes pallets and treated wood for furniture and other products.
The Associated Press contributed to this report.