Ariz. Rev. Stat. § 11-109
Maricopa county, the county seat of which is Phoenix, is bounded as follows:
Commencing at a point where the meridian line one hundred thirteen degrees twenty minutes west longitude, as defined by the Atwood survey of 1918, intersects the second standard parallel south, being the northwest corner of Pima county; thence north on such survey line and along the east boundaries of Yuma and La Paz counties to the point where the meridian line one hundred thirteen degrees twenty minutes west longitude, as surveyed, intersects the thirty-fourth parallel north latitude, as defined by the Thompson survey of 1924; thence east on the thirty-fourth parallel north latitude, as defined, and along the southern boundary of Yavapai county to the point where the Hassayampa river intersects such parallel; thence southeast in a direct line following the Thompson survey of 1924 to a point in the Agua Fria river two miles southerly and below the mouth of Humbug creek; thence northerly up the Agua Fria river to a point two miles southerly and below the place where the residence of J. W. Swilling stood on January 31, 1877; thence easterly in a direct line following the Thompson survey of 1924 to the point where the thirty-fourth parallel north latitude, as defined by such survey, intersects the Verde river; thence east on such parallel to the point where the parallel as surveyed intersects the summit of the Mazatzal range of mountains; thence southerly along the summit of the Mazatzal range of mountains to the point where such range of mountains intersects the centerline of the Salt river; thence easterly up the Salt river to the mouth of Tonto creek; thence southerly in a direct line toward a mountain known as the "Water Shed," and along the western boundary of Gila county to the point where such line and boundary intersects the north line of township one north; thence west on the north line of township one north and along the northern boundary of Pinal county to the point where such line intersects the eastern line of range seven east; thence south on the eastern line of range seven east to the point where such line intersects the southern line of township two south; thence west on such line to the point where such line intersects the Gila river; thence northerly and westerly down the Gila river to the point where the river intersects the eastern line of range one east, being the northwest corner of Pinal county; thence south on such line to the point where such line intersects the second standard parallel south, being the southwest corner of Pinal county; thence west on such parallel to the point where it intersects the meridian line one hundred thirteen degrees twenty minutes west longitude, as defined by the Atwood survey of 1918, being the place of beginning.
A.R.S. § 11-109