According to Official Guinness Records,
The largest hayride was achieved by 639 participants (all USA) at the Northwest Washington Fair in Lynden, Washington, USA, on 20 August 2011.
The hayride consisted of 10 hay-covered trailers pulled by a single snow plough. The ride lasted a total of 11 minutes 12 seconds.
For a complete list of 2011 records, please visit 2011 Guinness Records in United States.