Stealing some thunder from Two Rivers, WI, Ithaca NY has claimed itself as the birthplace of the Ice Cream Sundae, based on some very indepth research.
I know there are other towns that lay this claim, but it's definately clear that Ithaca, NY has the earliest documentation that the "sunday" (as originally spelled) was offered for sale at a soda shop owned by Chester Platt.
Both Ithaca and Two Rivers claim 1881 as the year of invention in their respective towns.
The problem with the story about Berner (in Two Rivers) creating the sundae in 1881 in his ice cream shop would be that Berner was 16/17 in 1881. Pretty young for a shop owner - even in the 1880's. Also, a 1939 Chicago Tribune article about the death of Berner said that the ice cream sunday was 40 years old. That would be 1889, not the 1881 as claimed by Two Rivers.
Never the less, the debate will rage on, but in my book, since Two River (and ever other town) does not have any documented proof of the sunday being sold prior to April 6, 1882 in their towns, Ithaca gets my vote.
However, since Berner use chocolate syrup, while Platt (in Ithaca) used cherry and cherry syrup, Two Rivers can say they invented the Chocolate Sundae.