Although the title Lord Eliot was in use much earlier, the peerage title Baron Eliot was formally created on January 13 1784 in the Peerage of Great Britain for Edward Eliot, later Edward Craggs-Eliot (July 8 1727 - February 17 1804). His son, John Eliot (September 30 1761 - November 17 1823), was created Earl of St Germans on November 28 1815, with which title the Barony then merged. Baron Eliot (or Lord Eliot) is customarily used as a courtesy title by the Heir Apparent to the Earldom.
Barons Eliot (1784)
Courtesy Usage of the title Lord Eliot