WIS-TV reported that Sheriff Daniel Simon said the shooting happened around 2:30 a.m. Sunday at a nightclub in Bishopville.
Simon said the club owner called authorities and said a young man was going to get a weapon.
Simon said a man fired shots at the building from across the street. A security guard returned fire and killed 23-year-old Timothy Stephen Kennedy.
Authorities said Kennedy was one of more than 200 people who had been at a birthday party at the club.
No other injuries were reported.
SLED and the Bishopville police are assisting in the investigation.