The castle complex, which included a towerhouse and adjoining farm buildings, was documented in two drawings by Beranger in 1766, offering us a glimpse of how the site appeared before its transformation. Today, only a single gate tower survives as testament to the castle's former presence, standing as a solitary reminder of centuries past.

The castle's history is well documented through various historical accounts, including Grose's illustrations from 1791 and Ball's extensive writings from the early 1900s. These sources paint a picture of a significant defensive structure that played its part in Dublin's medieval landscape. Archaeological surveys have confirmed the castle's position on relatively level ground, which would have provided clear sightlines across the surrounding countryside whilst maintaining proximity to the Dodder for water access.

At the beginning of the 18th century, Simmonscourt Castle met the same fate as many of Ireland's medieval fortifications; it was replaced by a Victorian residence more suited to the changing tastes and peaceful times of the era. This transformation marked the end of the castle's military significance, though the surviving gate tower continues to intrigue historians and visitors alike. The tower, catalogued as monument DU018-063002, remains accessible to those interested in exploring Dublin's medieval heritage, offering a tangible connection to the city's fortified past.