Built in 1611 by Sir William Stewart on his grant of 1,000 acres, this bawn represents a fascinating glimpse into the early days of the Plantation of Ulster. Stewart's original construction comprised a lime and stone fort with two flankers, complete with munition stores, a prison, guard rooms and a sentinel house; by 1619, he'd added a thatched dwelling within the walls that housed a Scottish minister and his family. Today, what remains are two rubble-built flankers and fragments of the connecting bawn walls, their weathered stones still bearing witness to four centuries of Irish history.

The surviving architecture reveals the defensive ingenuity of these frontier fortifications. The southern flanker, a two-storey circular tower standing roughly 4.5 metres high, perches dramatically above the shoreline with its battered base dropping steeply to the water below. Gun loops on each floor once provided covering fire for the eastern and southern walls, whilst timber-framed doors in the northwest gave access to each level. The northern flanker takes the form of a salient-angled bastion, slightly taller at 5.5 metres, with its ground floor accessible only from above; likely the very chamber described in 1611 as suitable for storing munitions or holding prisoners. Both structures retain evidence of their original timber joists and were topped with defensive parapets, whilst a surviving section of the western curtain wall still shows the chase for a timber door jamb and socket for a hefty draw bar.

Archaeological investigations in 1998 and 2005 revealed little beyond 18th and 19th century ditches in the vicinity, suggesting that much of the original plantation settlement has vanished beneath centuries of agricultural use. The fort's strategic position on Lough Swilly speaks to its original purpose as both a defensive stronghold and a symbol of English authority in newly planted Ulster. Though the eastern bawn wall depicted on early 20th century maps has disappeared entirely and nature has claimed much of what remains, Fort Stewart endures as a tangible link to the turbulent years when Scottish and English settlers first established themselves in Donegal, transforming the landscape and laying foundations for centuries of complex history that followed.