According to Official Guinness Records,
The greatest distance run on a treadmill in 24 hours is 261.18 km (162.29 mi), achieved by Luca Turrini (Australia), at the Fitness Show, Sydney Convention Centre, Sydney, Australia, on 29 May 2017.The attempt was a fundraiser to raise money for a children cancer charity.
For a complete list of 2017 records, please visit 2017 Guinness Records in Australia.