The current area of Kirkby is made up from the ancient parishes of Kirkby and Simonswood
The ancient system of parishes in England date back to before the Norman Conquest of 1066. Kirkby and Simonswood are thought to have been part of the parish of Walton-on-the-Hill prior to the Conquest (BHO).
“Kirkbye”, “Simons Wood foreft” and the “Alt flu” are first known to appear on the 1577 map of Lancashire (University of Lancashire) by Christopher Saxton (Wikipedia).
As of 1835, Kirkby (and presumably Simonswood) was part of the parish of Walton-on-the-Hill in the West Derby hundred, which also contained the townships of Walton-on-the-Hill, Formby, Everton, Bootle and Linacre, Kirkdale, Fazakerley, and West Derby (GENUKI).
Simonswood (and perhaps Kirkby) became a separate civil parish in 1866, likely as a result of the Poor Law Amendment Act 1866.
The Local Government Act 1894 converted all parishes to civil parishes, and it is the latest date when Kirkby could have become a civil parish. The accounts and minute book from the Kirkby Parish Council start at this time and can be found in the Knowsley Archives (paper catalogue reference KA70). The parish of Kirkby was in the Sefton Rural District from 1894 until 1922, and was then transferred to Whiston Rural District until 1958. The parish of Simonswood was part of the West Lancashire Rural District from 1894 until the rural district was abolished in 1974.
Kirkby Urban District was formed on 1st April 1958. A part of the parish of Simonswood covering the northern part of Northwood and the eastern part of Towerhill was transferred to the parish of Kirkby at this time. A further part up to the boundary of North Perimeter Road of the parish of Simonswood was transferred to the parish of Kirkby on 1st April 1966 (VoB, UK BMD). Kirkby appears to have become unparished as a result of the Local Government Act 1972, which led to the formation of the Metropolitan Borough of Knowsley and the abolition of Kirkby Urban District on 1st April 1974.
The original civil parish of Simonswood survived until the The Cheshire, Lancashire and Merseyside (County and Metropolitan Borough Boundaries) Order 1993, which abolished the parish of Simonswood in Merseyside (article 4) and established a successor parish of Simonswood in West Lancashire, with parts of the old parish covering Towerhill becoming part of the unparished Kirkby (article 5).
Kirkby remains unparished to this day, although the power to create a new civil parish council has existed since the Local Government Act 1972.