Pumpkin (jack-o’-lanterns) Guinness World Record: Boston, MA, October 21, 2006 With 30,128. Official.
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…by Anura Guruge
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So here is the final scoop so to speak. Keene, NH, on October 25, 2003 [i.e., 9 years ago], set the then official Guinness World Record with 28,952, for the 9th time in a row, the first record established by them in 1991 with just 600. See chart below.
But, 3 years later, the record was officially broken, with a certificate from Guinness to prove it, when 100,000+ people came together on Boston Common to light 30,128 jack-o’-lanterns — the event organized by the national ‘Camp Sunshine‘, a non-profit for Children.

Pumpkins in Boston in 2003, the skyline obviously very different from that of Keene. Picture from ‘outtamymindwithworry.blogspot.com’ — with THANKS.
Since establishing the then record in 2003, with its 28,952, Keene has managed to break the 29,000 mark twice, this year (2012) with 29,381 and 29,762 in 2009.
Wikipedia actually has a ‘Keene Pumpkin Festival’ page with lots of pertinent information. If you are still lusting for more information please visit them.
Here are the Keene pumpkin counts per the Wikipedia entry: