Police said they searched Templemore sports complex last Thursday - when the centre was used for an election count - after a coded warning about a bomb.
But they said the original information was misleading.
They said the device, hidden in the ceiling of toilets, did not contain a detonator and could not have exploded.
The device was discovered after a caller contacted a parochial house in Derry
Last Thursday, a pipebomb was left in a taxi outside the same building.
In a statement, dissident republicans Oglaigh na h'Eireann said the two devices were left on Thursday and that a warning had been given.