Sprinkler City
n. A fast-growing outer suburb or exurb.
Examples
2003
Remember Angry White Males? And Soccer Moms? There's now an army of these goofy subgroups marching around in the minds of political consultants.

According to The Times, pollster Mark Penn urged Democrats last spring to focus their attention on capturing the votes of Office Park Dads — suburban white fathers between the ages of 25 to 50 who own stock. Competing advice came from Celinda Lake, who said the focus should be on NASCAR Dads — church-going gun owners who like stock-car racing.

The GOP's grip on reality isn't much better. Republicans were told to pursue Patio Man (fond of fancy grills) and his wife (Realtor Mom), who live with their kids in Sprinkler City (the outer suburbs).
—Daryl Lease, “Exploring for campaign cash,” Sarasota Herald-Tribune, January 13, 2003
2002 (earliest)
Sprinkler Cities are also generally the most Republican areas of the country. In some of the Sprinkler City congressional districts, Republicans have a 2 or 3 or 4 to 1 registration advantage over Democrats. As cultural centers, they represent the beau ideal of Republican selfhood, and are becoming the new base—the brains, heart, guts, and soul of the emerging Republican party. Their values are not the same as those found in either old-line suburbs like Greenwich, Connecticut, where a certain sort of Republican used to dominate, or traditional conservative bastions, such as the old South. This isn't even the more modest conservatism found in the midwestern farm belt. In fact, the rising prominence of these places heralds a new style of suburb vs. suburb politics, with the explosively growing Republican outer suburbs vying with the slower-growing and increasingly Democratic inner suburbs for control of the center of American political gravity.

If you stand on a hilltop overlooking a Sprinkler City, you see, stretched across the landscape, little brown puffs here and there where bulldozers are kicking up dirt while building new townhomes, office parks, shopping malls, AmeriSuites guest hotels, and golf courses. Everything in a Sprinkler City is new. The highways are so clean and freshly paved you can eat off them. The elementary schools have spic and span playgrounds, unscuffed walls, and immaculate mini-observatories for just-forming science classes.
—David Brooks, “Patio Man and the Sprawl People,” The Weekly Standard, August 12, 2002
Notes
The phrase Sprinkler City (or the more generic sprinkler city variation that we're starting to see; the move to all-lowercase is always a good sign for the longevity of a new term) is the invention of journalist David Brooks (see the earliest citation). Brooks, an avid and clever neologist, is also responsible for bobo (bourgeois bohemian) as well as the new demographic labels Patio Man and Realtor Mom that are mentioned in the first example citation.