Historical records describe it as a rectangular structure flanked by two circular towers at its northern corners, connected to the main castle by a defensive wall or ditch; possibly the 'great fosse' mentioned in various documents. This fortification helped create a riverside bawn, essentially a fortified enclosure that protected the approach to the castle from the Shannon River.

By 1581, the tower had already fallen into disrepair when Thomas, Earl of Ormond and Ossory, received a crown grant for 'an old ruinous tower called Connaghte tower covered with straw'. The grant included a 27-metre parcel of land to the south, a garden plot with ruined cottages to the north, and land stretching through the great fosse westward to the River Shannon. The tower's military significance came to a violent end during the Williamite War in Ireland, when artillery bombardment in 1691 left it partially demolished.

Despite the damage, remnants of the Connacht Tower persisted for another century and a half. Thomas Sherrard's 1784 map of Athlone still shows its partial remains, and local historian Langrishe noted that ruins survived until the mid-nineteenth century. The tower's final demise came not from warfare but from progress; it was removed during the Shannon navigation improvements and the construction of Grace Road. Today, no visible trace remains of this once-important defensive structure that guarded Athlone's western approaches for centuries.