A man in his 70s, who was a pedestrian, died following a crash involving three vehicles near Ballyhornan village.
In Dungannon, Phelim Brady, 69, died following a collision between a tractor and a lorry on the Killybracken Road.
On Tuesday evening,  man in his 80s died after it is believed he was struck by a tractor at a farm on the Loughnamarve Road, Pomeroy.
The Health and Safety Executive are investigating the accident.
Police said a 30-year-old man has been arrested for a number of offences in connection with the crash near Ballyhornan.
A 19-year-old man believed to have been involved in the accident was taken to a nearby hospital for injuries, that are not believed to be life-threatening.
Meanwhile, police said two men, aged 50 and 43, have been arrested in connection with the crash near Dungannon.
Police have appealed for witnesses to any of the incidents to contact them.
Three elderly men have been killed in separate traffic accidents in Counties Down and Tyrone.