Donogh O'Brien, 4th Earl of Thomond and Baron Ibrickan, (died 1624) was a Protestant Irish nobleman and soldier. He fought for Queen Elizabeth in the Nine Years' War (Ireland) and participated at the Siege of Kinsale. His long-term objective, achieved after decades, was to obtain an official acknowledgment that County Clare, where his possessions were situated, was part of the Province of Munster, to free it from the jurisdiction of the Connaught government under which it had been placed.