Buchanan said Mercer was on his way home from work when the GMC work pickup he was driving west into Charles Town collided head-on with a Ford Explorer that was eastbound on W.Va. 9.
The crash, which was reported about 3:30 p.m., occurred near the Crosswinds subdivision, police said. The accident closed the two-lane stretch of W.Va. 9 at the top of a hill for three hours, police said.
Mercer and the driver of the Ford Explorer, John Janszen, had to be cut from their vehicles, said Cpl. Melissa Kerns of the Charles Town Police Department.
Janszen, 35, of Harpers Ferry, W.Va., was treated at Washington County Hospital and released, a hospital spokeswoman said Sunday night.
Angela Janszen, 31, of Harpers Ferry, was treated at Jefferson Memorial Hospital in Ranson, W.Va., and released, a hospital spokeswoman said.
Conditions of a 12-year-old male passenger in the Explorer and an 8 year-old female passenger were not available Sunday night.
Valerie Williamson, the driver of a third car, a Honda CR-V, was treated at Jefferson Memorial Hospital and released, the spokeswoman said. Williamson, 45, is from Ashburn, Va.
It is unclear what caused the wreck. A Charles Town Police Department spokesman said Sunday that no additional details would be released until today, when Police Chief Mike Aldridge returns to work.
Mercer was married, and he and his wife, Lavonda, had four children, Buchanan said. The children included 1-year-old twins, a boy and a girl; a 5-year-old son; and an 11-year-old daughter. Mercer had a 13-year-old daughter from a previous marriage, Buchanan said.
Mercer, who grew up in Frederick, Md., and the Charles Town area, was a deacon at the Word of Faith Tabernacle in Kearneysville, W.Va., Buchanan said.
"His business, his family and his church came before anything," Buchanan said.