The Ainsty is a compact territory with ancient origins. It lies to the west of York and its boundaries are clearly  defined by three rivers;  the Nidd to the north, the Ouse to the east and the Wharfe on the south.  A narrow land boundary on the west runs between Cattal bridge on the Nidd to the township boundary between Thorp Arch and Wetherby on the Wharfe.  Thirty five villages are within its bounds and it has a circuit of 32 miles.

The Ainsty in 1735
Part of a map published in 'Eboracum' by Francis Drake

Long ago the Ainsty was a wapentake, an administrative area, and the now vanished Ainsty Cross on the old Roman road (now the A64) at Streethouses, near Bilbrough marked the place where the wapentake courts were held.  There was another Ainsty Cross, marking the western land boundary between the Wharfe and the Nidd. 

There is nothing to tell us of the Ainsty in earlier times: it may have already been a territorial unit before the Romans arrived, if not, they may have seen the value of it, driving their road through it and clearing land along it for agricultural purposes, to feed the growing city of York.  The place names show a mix of Roman, early English and Scandinavian influences.   The Normans certainly knew it as a territorial unit and it is recorded as such in the Domesday book.

Even before its annexation to York in the 15th century, the Ainsty gravitated towards the city; it was a natural hinterland, an area with good agricultural land and communications, and an important commercial centre.  York often laid claim to the Ainsty but it was not formally annexed until 1449 when it became known as the county of the city of York.  Traditionally the lord mayor and corporation of York met important visitors on Tadcaster bridge, on the western boundary of their territory, and then processed with them along the Streete to York.

In the 16th and 17th centuries musters of local men for military purposes  took place in various locations e.g. Colton Moor, Hutton Moor, on the Knavesmire or at York Castle.  The men of the Ainsty were summoned to march with the men of York to Scotland, or the east coast, when the safety of the realm was endangered.  The Ainsty had its own chief constable and  Quarter Sessions, which were held alongside those for York; the jury was made up of Ainsty men and each parish constable was required to attend.
 
In 1835, the Municipal Reform Act ended the long association of the Ainsty with the city of York and placed it in the West Riding.  Later, 20th century boundary changes moved it into the North Riding.