Formerly a township in Addingharn parish, has, according to the Local Government Act of 1894, been constituted a distinct civil parish, but for all ecclesiastical matters it remains united with the above mentioned parish. It covers an area of 1,581 acres, of the following ratable value: land, £1,435; buildings, £471; and had in 1891 a population of 161. Glassonby is comprised within Leath ward and petty sessional division; the deanery of Penrith E.; the poor law union, rural and county court districts of Penrith; and the county council electoral division of Edenhall. The soil is generally fertile, and in a high state of cultivation.

The manors of Glassonby and Gamblesby were formerly united in one lordship, which was given by Henry I. to one Hildred, to be held of the Crown by the payment of 2s. cornage. Hildred's line terminated in a daughter, who brought the manors in marriage to William de Ireby. In like manner they passed by female heirs to the Lascelles and Seatons. Christopher de Seaton having espoused the cause of Robert Bruce, his estates were forfeited to the Crown, and the lordship of Gamblesby-with-Unthank and other estates in this county were given by Edward I. to William Latimer. From this family they were carried by the marriage of the heiress to John Neville, father of Ralph Neville, Earl of Westmorland. The manor of Gamblesby is now the property of the Duke of Devonshire, having been purchased from the Duke of Portland in 1787. From the Nevilles, Glassonby passed by marriage to the Dacres, and in 1715 it was purchased of the co-heiresses by Sir Christopher Musgrave, Bart., and still remains in that family. The land is partly freehold and partly customary, the latter tenants being subject to the payment of a small lord's rent. The most extensive landowners are Sir R.G. Musgrave, Bart., and W.E. Rowley, Esq. The village of Glassonby occupies a pleasant situation on the crest of some rising ground, about eight miles N.E. by N. of Penrith.

The Church, dedicated to St. Michael, is situated about a quarter of a mile from the village. The list of vicars may be traced as far back as 1292. The present church belongs probably to the 15th or 16th century, though no doubt many of the stones used in erecting it are of a much older date, and had most likely been used in a former building, which tradition says was nearer the east bank of the river Eden. The communion plate includes a silver chalice dated 1612. The paten was the gift of a Mr. G. Lumley, and belongs to the reign of Queen Anne. In the churchyard there stands the head of an ancient cross, probably of Saxon origin, and no doubt brought thither from the site of an older church. Two fragments of an ancient cross, of unique design, stand at present in the porch. The church underwent considerable alteration and restoration in 1898 at a cost of £500, when the chancel roof was rebuilt. The old flat white-washed ceilings were removed, and an oak ceiling of rounded form placed in the chancel, and a ceiling of plaster with Canadian redwood moulding in the nave. The vestry roof was raised and a new chamber for the organ provided by taking down part of the north wall of the chancel. An ornamental arch of plaster in imitation Norman style was removed, and the stone arch, which was erected in 1786 to support the newly-raised roof, exposed and re-dressed. The chancel was also repaired and the sanctuary paved with black and white marble. The presentation was vested in the lords of the manor until 1245, when Christian, widow of Thomas de Lascelles, granted it to the priory of Carlisle. This grant was confirmed to the prior and convent by Bishop Irton, in 1282, who ordained that the grantees should make sufficient provision for the maintenance of the vicar, and the celebration of all religious rites with due solemnity. In the Valor of Pope Nicholas (1291) this church is returned as worth £40; in a valuation made in the reign of Edward II. it is put down at £10; and in the King's Book at £9 4s. 7d. About 1678, the dean and chapter, to whom the patronage was granted after the dissolution of the priory, granted a lease of the tithes of Little Salkeld in augmentation of the living, which is now valued at £330. The benefice has been held by some eminent churchmen. Bishop Nicolson, of Carlisle, afterwards Archbishop of Cashell, held the vicarage previous to his elevation to the episcopate; and Dr. Paley, author of the "Evidences of Christianity," and many other works, was vicar of Addingham from 1792 till 1805. A document is still in existence, dated 1786, in which an agreement is made to re-roof the church and erect a chancel arch for the sum of four guineas.

The Wesleyan Chapel was erected in 1869, at a cost of £324, raised by subscription. It will accommodate 120 persons.

Maughanby is a hamlet in this parish, seven miles N.E. of Penrith. A Free School was erected here as early as 1634, by the Rev. Edward Mayplett, prebendary of Carlisle and vicar of the parish. He endowed it with a house and 76 acres of land, then worth about £10, but now let for £97 10s. By a bond dated 1676, the master is required to attend the church regularly with his scholars, and to instruct them in the principles of religion, especially the catechism of the Church of England. A new school was erected in 1868, in a more central situation, at a cost of £800, including residence. The ancient institutes of the school have been remodelled by the Charity Commissioners. According to the revised scheme, £25 of the income is appropriated to the Mayflett Exhibition, in memory of the pious founder, tenable for three years in some place of higher education. The school was placed under Government inspection in 1877.

Whilst some excavations were being carried out in 1900 in a field belonging to W.E. Rowley, Esq., a beautiful urn of ancient British manufacture, and a blue and white bead were turned out of a barrow or mound. They have been placed in the museum at Tullie House, Carlisle.