The Shire of Irwin is a local government area in the Mid West region of Western Australia, about south of Geraldton and about north of the state capital, Perth. The Shire covers an area of , and its seat of government is the town of Dongara.
The Irwin Road District was created on 24 January 1871 as one of the first regional local government areas in Western Australia. Before this, it was the "Victoria District". On 16 June 1916, Irwin received a large land area from the Upper Irwin Road Board shortly before that entity's dissolution. Sections of the district separated as part of the formation of the Carnamah Road District on 24 August 1923 and the Three Springs Road District on 2 November 1928.
On 1 July 1961, it became a shire following the passage of the Local Government Act 1960, which reformed all remaining road districts into shires.
In June 2015, Irwin declared itself gasfield free.
The Shire is divided into four wards:
The towns and localities of the Shire of Irwin with population and size figures based on the most recent Australian census:
As of 2023, 157 places are heritage-listed in the Shire of Irwin, of which 16 are on the State Register of Heritage Places.