According to Official Guinness Records,
The most participants in a badminton rally is 123 and was achieved by Meath Badminton Association (Ireland) in Navan, County Meath, Ireland, on 21 November 2014. The record raised funds for the Friends of Frank charity and for the participating clubs.
For a complete list of 2014 records, please visit 2014 Guinness Records in Ireland.