What it means
Annexation is how an Arizona city grows: it absorbs unincorporated county land, parcel by parcel, and the land becomes city. Scottsdale is the Valley’s clearest case. It incorporated on June 25, 1951 on about one square mile around the old townsite and now covers 184.5 square miles, 31 miles from the Tempe line to Carefree Highway, nearly all of it annexed. When a longtime resident says “that was county when we moved here,” they mean the land had not yet been annexed; when a neighbor says “we’re in the county,” it still has not.
That second case is a county island: a pocket of unincorporated land the city grew around and never took, still governed by Maricopa County, with county zoning, county roads and Sheriff’s deputies, while city services run past the fence. The annexation guide tells how the city grew; the unincorporated county guide explains life on the other side of the line.
Where you’ll meet it
On the city limits map, which has holes and notches where you would expect a border; in Rio Verde Foothills, the unincorporated community whose 2023 water cutoff made the distinction world news; along Scottsdale Road north of Cactus, where the west side of the street is Phoenix; and in the county’s tax-levy list, which includes a fire district for islands in Scottsdale’s planning area.
Where the word came from
The machinery is in ARS 9-471, and it runs on owners, not voters. A city files a blank petition describing the area with the county recorder, waits 30 days, holds a public hearing, then gathers signatures. The petition succeeds when it carries owners of at least half the assessed value of the property and more than half of the property owners; the area must touch the city for at least 300 feet and be at least 200 feet wide; the owners have a year to sign; and then the council adopts an ordinance. Because value counts as well as heads, one rancher can bring in a square mile on one signature, while a subdivision takes a campaign. Residents get no vote.
Scottsdale used that machinery like a weapon. Phoenix was annexing hungrily in the 1950s, and a town that stood still would be surrounded. Three ordinances in 1962 and 1963 swept in some 41 square miles, including the old Thunderbird II airfield; Phoenix sued over the map and lost. On January 30, 1964 the two councils adopted matching resolutions making Scottsdale Road the boundary from Cactus Road north to Jomax: Phoenix west of the road, Scottsdale east. Paradise Valley had already incorporated on May 24, 1961 to escape both, and the Salt River Pima-Maricopa Indian Community, a sovereign nation, fixed the east. So the city went north: McCormick Ranch in 1967, East Shea in 1975, and under Mayor Herb Drinkwater about 80 square miles of desert between 1981 and 1984, ending with the 36 square miles that took effect on August 1, 1984 and reached the Tonto National Forest. Carefree incorporated that year to stop the advance.
The county island is annexation’s leftover. Every time the city took the willing parcels and skipped the unwilling ones, it left pockets behind. The legislature eventually noticed: 9-471 now bars an annexation that would completely surround county territory unless the county board finds it will not hurt county services, with an exception for land the city already surrounds. The islands that exist keep county rules, and their residents can form a county island fire district to pay for fire protection.
What it is not
Annexation is not incorporation. Incorporation creates a new town; annexation enlarges an existing one. Nor can a county island simply incorporate its way out: under ARS 9-101.01, territory within six miles of a city of 5,000 or more needs that city’s approval, or the city’s refusal to annex it, before it can form a town of its own.
The fine print
The statute’s small rules decide real fights. The 300-foot contiguity rule stops a city leaping across the desert to grab a distant resort; the 200-foot minimum width stops “strip” annexations that run a thin line of road to a prize parcel. The 30-day wait and the public hearing in its last ten days are the only moments residents are guaranteed a say, which is why Scottsdale’s annexation fights happened at hearings, not polls.
The 1964 line explains more of the modern map than any other single fact. The Airpark, Kierland and every “Scottsdale” address whose neighbor across Scottsdale Road pays Phoenix taxes sit on it. Postal zones do not match city limits, which is why a mailing address proves nothing.
Rio Verde Foothills is the lesson in what annexation leaves behind. It was never annexed, grew through lot splits of five or fewer parcels that escaped the state’s 100-year water rule, and relied on water hauled from a Scottsdale standpipe until the city closed it to non-residents on January 1, 2023. The city’s duties stop at its limits; the county’s begin there. Annexing the remaining islands comes up at council every few years and goes nowhere, because it needs the owners’ signatures and island residents like county zoning. The north-versus-south entry explains what the annexed desert became; state trust land explains the parcels the city still cannot touch.