The fictional Middle-earth land where the Shire is located in J.R.R. Tolkien’s works is Eriador.
Eriador is the broad region west of the Misty Mountains and east of the Blue Mountains. It includes the Shire, Bree-land, Rivendell, the Trollshaws, and the ruins of the northern kingdom of Arnor. Much of The Lord of the Rings begins in this part of Middle-earth, as Frodo leaves the Shire and travels toward Rivendell.
The Shire is therefore a country or region within Eriador, not a synonym for the whole area. Tolkien’s maps show Eriador as a large landscape containing several distinct peoples and territories. The region had once been more politically organized under Arnor, but Arnor declined and eventually disappeared.
Eriador also contains important ancient sites, including the Barrow-downs and Weathertop. These locations connect the peaceful opening of the story with the older history of Middle-earth.