Today, I managed to get hold of a copy of the first edition of Walton Burgess’s Five Hundred Mistakes of Daily Occurrence in Speaking, Pronouncing, and Writing the English Language, Corrected, New York. It was published in 1856, and it is, to my knowledge at least, the first American English usage guide. The text itself can be found in Project Gutenberg, and I refer to it in my Introduction to Late Modern English (Tieken-Boon van Ostade 2009:5; Edinburgh University Press).
I’d be interested to hear if other people have written about it.
The book is also available, in pdf, in Google Books. (Thanks to Robin for this.)