Sinn Fein Councillor Tony McCaul, who was arrested on Thursday as part of a police investigation into paramilitary activity in the Dungiven area, was released unconditionally late on Thursday.
Sinn Fein said the 62-year-old, who was elected to the shadow Causeway Coast and Glens Council in May and who sits on Limavady Policing and Community Safety Partnership, was released shortly before 11pm.
Three other men arrested as part of the same investigation, aged 58, 31 and 31, were also released unconditionally on Thursday evening, police said.
The men were arrested at properties in the Foreglen and Claudy areas on Thursday morning by Serious Crime Branch detectives, who also carried out a series of searches during the operation.
Police said they were investigating paramilitary activity, including shootings and threats, predominantly over the past four years.
The men were questioned at Antrim police station.