On October 12, 1812, Brock puts pen to paper to begin a letter to Sir George Prevost. This may have been the last letter Brock wrote. He writes:
The vast number of troops which have been this day added to the strong force previously collected on the opposite side, convinces me, with other indications, that an attack is not far distant. I have in consequence directed every exertion to be made to complete the militia to 2,000 men, but fear that I shall not be able to effect my object with willing, well-disposed characters. Were it not for the numbers of Americans in our ranks, we might defy all their efforts against this part of the province.