The Dissolution came into effect for Cleator church c. 1539. In 1541, the parish was brought into the diocese of Chester, but in 1856 this was changed to the diocese of Carlisle. The original parish was later divided, in 1870, with the creation of a church at Cleator Moor, which grew up as a result of the iron industry. Only the chancel of St Leonard’s Church is medieval, the nave having been rebuilt and enlarged in 1841. In the late 18thc, the walls of the chancel were raised about two feet, new pews were installed and the church was repainted, along with other changes. Little is known about the early cross at Cleator, except that it was found in the walling around the churchyard (this cross should not to be confused with the so-called ‘Fawn Cross’, which is later). In the N wall one Norman window survives, though at a later date it was partially opened out on the exterior to let in more light. The church was largely restored in 1900-1903, when a new vestry, baptistry and porch were built. At the same time remains of a piscina were found in the S wall of the chancel. A carved animal also survives on a corbel stone on the SE exterior corner of the chancel.

The Domesday Survey did not cover this part of England. Cleator’s overlord was the baron of Copeland/Egremont, which was given by Ranulph de Machines to his brother William in about 1120. Richard of Cleator (‘Ricardo de Cleterche’) is the earliest known lord of the manor of Cleator, mentioned for the first time in the late 12thc. Richard appears to have been the son of Anketell. The latter's father was Durand, who seems to be the same knight recorded with King David I of Scotland at Lamplugh when that king granted a charter to St Bees (the charter must date to the period 1136-1153). King Henry II took back control of these lands from Scotland in 1157. Richard of Cleator’s brother, Nicholas, is recorded as ‘Nicholao persona’, and this has been interpreted as the first reference to the church at Cleator, ‘persona’ seemingly meaning ‘parson’. The rectory of the church at Cleator was held by Calder Abbey, founded 1134/5 as an offshoot of Furness Abbey. It is uncertain when the church at Cleator came into the possession of the monks of the abbey, as the chartulary for Calder Abbey no longer exists, but it was recorded at the Refomation as being in their possession. The first monks of Calder Abbey stayed for only four years, being forced out when the abbey was sacked by invading Scots. These monks then moved to several places, eventually settling at Byland. Only in 1142/3 was there a re-foundation of the abbey at Calder, when a new group of monks from Furness moved back to the site. The Savigniac order merged with the Cistercians in 1147 (though at Calder, as at Furness, this may not have taken effect until 1148). In the Papal Tax Roll of 1291-2, the church at Cleator was assessed at £4. 13s. 4d. It is listed there as ‘Ecclesia de Cleter’, within the deaconry of ‘Couplandie’ (i.e. Copeland/Allerdale-above-Derwent). In or around 1315, James Douglas attacked and burned the manor of Cleator, but there is no mention of an attack on the church. Further work on the church was carried out in the 15thc, as evidenced by the surviving S windows of the chancel and by the discovery, in 1900-1903, of earlier sections of an E window. There is a variety of medieval spellings for Cleator, including ‘Cletergh’, ‘Cleterche’, ‘Cleterne’, ‘Cletour’ and ‘Cleter’.

In 1916, Caine wrote that the section of cross had been built into one of the churchyard walls and suggested it originally formed part of a grave cover. This use is unlikely, however, as the cross is carved on both sides. Caine also listed it as 13thc. In 1958, Butler suggested that the cross was early Norman and in 1988 Cramp suggested a date of late 11thc to mid 12thc for the cross. Ryder and Cramp both suggested that the cross was originally used as a head stone. When the piscina was discovered in the restorations of 1900-3, it was proposed that it was contemporary with the walls, which appear to be part of the Norman church, and therefore contemporary with the north window of the chancel. Martindale suggested a date for this part of the church as early 12thc. During the 20th-c restorations, it was discovered that the interior walling at the lower level was built of ‘round cobbles’ above which was dressed stone. The question arose as to whether this was part of an earlier church. Others have suggested that this was part of the 12th-c church. The exterior of the chancel shows numerous changes, including a difference in stonework at various levels. The carved animal on the SE corner is enigmatic and its date uncertain. It has been suggested that it was one of the early corbels before the walls of the chancel were heightened in the 18thc.