He was a delegate from Goliad to the Convention of 1836 at Washington-on-the-Brazos and there signed the Declaration of Independence. When the convention was dissolved he hastened to rejoin the military forces. While serving as aide-de-camp to Thomas J. Rusk, Mottley was mortally wounded in the battle of San Jacinto; he died on the night of April 21, 1836, and was buried on the battlefield. His heirs could not be located, and his donation certificate for military service was sold at auction. Motley County, misspelled, was named in his honor.
NoteThis is a cenotaph. His name is incorrectly inscribed as William Junius Mottley. In 1881, a decision was made to place permanent memorials at the graves of those men who had been killed in the Battle of San Jacinto and buried on the battlefield. It was discovered, however, that all of the original wooden grave markers, except for Benjamin Brigham's, had rotted away and no one could remember exactly where the others rested. As a compromise, since the soldiers had been buried closely together, it was decided to place a cenotaph over Brigham's grave as a memorial to all of them.
29° 45.232, -095° 05.363
San Jacinto Battleground State Historic Site