According to Official Guinness Records,
The longest marathon playing wiffleball is 26 hr 21 min 10 sec and was achieved by ten players led by Tom Johnson (all USA) in Duluth, Minnesota, USA, on 7-8 July 2017. The players on team Tommy consisted of Tom Johnson, Leo Johnson, Josh Finner, Kevin Johnson, and Dale Zubke. The players on team Rev consisted of Dave Engstrom Jr., Mike McDevitt Jr., Brad Gantt, Matt Haedrich, and Corey Verhel. They all played to bring awareness and to raise funds for The Alzheimer's Association.
For a complete list of 2017 records, please visit 2017 Guinness Records in United States.