The parish of Milltown is made up of the two civil parishes of Adergoole and Liskeevy, both of which are of medieval origin. The first historical record of Milltown dates back to 1589. According to historian Hubert Thomas Knox's History of Mayo, Sir Murrogh O'Flaherty and his army came to attack Edward Birmingham. They stormed the castle, burnt half of Milltown and destroyed the castle's corn, but still failed to capture the castle after a bloody battle. On their return to Cong, they burnt sixteen other villages and seized three thousand cattle.

The placename of Milltown or Baile an Mhuilinn (the town of the mill), is derived from the two mills located on the River Clare - O'Grady's mill at Milltown, and Birmingham's mill at Lack. O'Grady's mill was demolished in the 1950s during the Corrib River Drainage Scheme, while the ruins of Birmingham's mill can still be seen along the river. The Birmingham mill was a corn and tuck mill. It was noted in the valuation office Mill Brook records of the 1850s as having one pair of mill stones, a water wheel of 14 feet in diameter and valued at £2. The resident miller at the time was John Farrell.