The attack happened in the Monkey Lane area of Cookstown.
Detective Sergeant Olphert said: “At around 2am, it was reported that two males approached a female in the Monkey Lane area.
“The two males are reported to have carried out a series of serious sexual assaults on the female.
“CCTV enquiries in the area show that the two males then left the area towards Burn Road.
“The woman was left badly shaken but not physically injured.
“Enquiries are continuing and we would appeal to anyone who witnessed the incident or who observed two men and a woman in the Monkey Lane/Central Avenue at this time to contact detectives on 101, quoting reference number 343 13/7/19.
“Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111 which is 100% anonymous and gives people the power to speak up and stop crime.”