I don't know if this helps, but I checked the US Army Register of Enlistments 1798-1914 and found the following: Entry #5748: William Williams, PVT, 19 USI (US Infantry), enlisted Feb 25 1814, Capt. Trimble's, (doesn't specify if Capt. Trimble had a regiment or comapny), died of wounds Sept 3 1814, remarks: see pension case. This register did not list a pension file number so checked the War of 1812 Pension Index and didn't find any file that fit your ancestor, but since it appears that his family went to court for it, it would probably be in a different file in the National Archives.However, the fact that the enlistment register makes note of it means that it did/does exit. You will probably be able to find a service record for him as well at the National Archives, at least you have an enlistment date. Unlike most of the other entries in the book, it did not give a place of birth or place of enlistment. Good luck.