Inside the W tower of St Mary's Church, Harrington are two stones and a doorway which have been said to date from the 12th century. One is a capital, another a grave cover and the third parts of a later-widened doorway. The base of the W tower may also date from this period, but there are no diagnostic features. The rest of the church is later, rebuilt in 1634 and again in 1884-5. In 1860, prior to the extensive rebuild some 25 years later, the church was described as 'consisting of nave and chancel, with square western tower' (Wellan, p. 395). The W tower was re-built in 1905-7. After the Reformation, the advowson of the church was given to Robert Brokelsbye and Thomas Dalston. About 1564 the advowson and right of patronage passed to Henry Curwen. Thereafter, it continued to remain in the Curwen family. The town centre of Harrington is now based on the port of Harrington, but this was not the case in the medieval period, as the port and town were built after 1760. St Mary's Church is sited further away from this, in the area sometimes referred to as 'High Harrington'.

Harrington appears to be pre-Norman in date, but it is only first documented in the 12th century. In medieval documents, the name appears as ‘Hafrinctuna’, ‘Haverington’ or versions of these. At an uncertain date between the mid-12th century and 1179, Gospatric son of Orm gave the church of Harrington to St Mary’s Abbey in York, and sometime between 1154 and 1181 the chapel of Harrington (‘capellam de Haveryngton’) was confirmed to St Bees’ Priory by the Archbishop of York. St Bees’ Priory had been founded in the early 1120s and was a cell of St Mary’s Abbey. Thomas son of Gospatric of Workington, confirmed the gift of the church of Harrington made by his father. Witness to the same document was Robert of Harrington (Haveringtuna), who was the first person known to take on the family name of Harrington. This must have occurred before 1200, as Thomas son of Gospatric appears to have died at the end of that year. In a seperate charter, Robert of Harrington also confirmed the gift of the church of Harrington to the Priory of St Bees. The manor of Harrington remained in the hands of the same family for several centuries, until finally being forfeited to the crown. In the Taxatio Ecclesiastica of 1291, the patronage of the ‘Ecclesia de Han’ngton’ is listed as part of the deaconry of Copeland (Couplandie).

Capital: Within Cumbria, there are stylistic comparisons for the Harrington capital decoration, with leaves growing off of long stems. These include the broken font found re-used in the walls of St Bridget's Church in Beckermet, The N doorway capitals at Bowness-on-Solway, and on the end of a small grave cover inside Bromfield church. All of these may be late-12th century.

Grave Cover: The grave cover is not of the usual form for the post-1066 period, but the inclusion of shears is a later feature. Butler (p. 215) seems to put the Harrington example into a late-12th century context.

Imposts of doorway: This type of impost begins to appear in the later part of the 12th century, and can be seen in modern-day Cumbria at such places as Barton (piscina), Barrow in Furness (Furness Abbey), Broughton-in-Furness (S doorway of church), and Millom (N doorway of church). All of these are found in association with waterleaf capitals. The W side of the inner arch at Broughton-in-Furness is very close in form to that at Harrington. At Broughton, the doorway has two two orders, which may help explain the rough stone around the edges of the Harrington doorway and curious vertical line along the N jamb. These may suggest that it, too, originally had at least two orders. A date in the late-12th century for the Harrinton doorway (before widening) seems a real possiblity. It is thought that the doorway was widened about the time that extensive work on the church was carried out in 1634. The medieval font was found built into the W tower at this time and subsequently carved witht the date 1634.

Gospatric son of Orm was active in the years between 1145/7 and 1179. Copeland was part of that land which was ceded to King David I of Scotland in 1136 and remained in Scottish royal hands until recovered by King Henry II in 1157. Gospatric son of Orm was a witness to the foundation charter of the Abbey of Holm Cultram, founded by the Scottish Royal family in about 1150.