They said she was Nikita Johnson, aged 23, from Rotherham.
A short statement from the force said: "Nikita's family are being supported by specially-trained officers at this difficult time."
The M18 was closed for a number of hours on Saturday morning after South Yorkshire Police said 'a body was found' on the carriageway at junction 1.
The emergency services were called to the carriageway, near Bawtry Road, at around 2.45am. The bridge across the motorway was also closed as police investigated.