This is an excellent question, which has a fairly complicated answer. So we’ll start at the beginning.
There are three incorporated cities in Las Vegas Valley: Las Vegas, North Las Vegas, and Henderson. The rest of the Las Vegas area is officially unincorporated; Clark County provides government and municipal services to nearly 750,000 county residents, compared to the nearly 900,000 people who live in the cities.
However, there are other geopolitical designations in the Las Vegas Valley. The three "townships" are the Las Vegas Township, the North Las Vegas Township, and the Henderson Township -- yes, the same as the three cities, but they have different boundaries, which delineate the jurisdictions of the state courts.
A third political subdivision is the "unincorporated town." There are six of these: Enterprise, Spring Valley, Sunrise Manor, Whitney, Winchester, and, of course, Paradise.
The six unincorporated towns are incorporated, so to speak, within the Las Vegas Township (a couple have edges that jut into the Henderson and North Las Vegas townships).
The post office, it seems, follows the township divisions. For example, a "Las Vegas" resident to the post office can live in Paradise, which is in the county and has nothing to do with the City of Las Vegas at all, but does fall within the Las Vegas Township. (There’s no Paradise town address or zip code.) So a southern Nevada resident can live in a city and a township at the same time, or in a town and a township at the same time, but not a city and a town at the same time, even though the post office considers all the towns to be in the cities.
To further complicate matters, there are also named "unincorporated areas" in the valley, such as Lone Mountain, that don’t qualify as official towns, since the county hasn’t granted town status to them (either because the county hasn’t approved submitted petitions or because the residents haven’t petitioned the county government for official status).
As far as services go, combined county and city services include public schools, health, water, and flood control. Las Vegas and Clark County share law enforcement and libraries, though North Las Vegas and Henderson have their own police and fire departments and library districts. Las Vegas and Clark County have separate fire departments. The towns, though falling within the Las Vegas Township, are governed by the county; they vote for county commissioners, not city councilors, and everything from animal control to parks and public works are administered by the county.
Unincorporated towns have voluntary "town advisory boards" that confer with the Clark County Commission on town issues, such as zoning and planning. In addition, town (that is to say: county) homeowners and landowners pay less in property taxes than their city counterparts.
Lowered taxes were a beneficial unintended consequence of the inception of unincorporated towns, whose main reason for being started out during jurisdiction, annexation, or service conflicts with the cities. Paradise, for example, was formed way back in 1950, at a time when the City of Las Vegas was launching an attempt to annex the incipient Las Vegas Strip. But the casino bosses had built their resorts way out in the desert specifically to avoid city regulation and taxation, so they petitioned the county commissioners to form the town of Paradise to block the city’s land grab. The commissioners quickly saw an opportunity to expand the county’s own fledgling tax base and granted unincorporated-town status to the Strip, forever blocking the city from acquiring it.
The town of Winchester to the east of the Strip was created in 1953, splitting the big -- and growing -- town of Paradise in two. Sunrise Manor was created in 1957 to fight annexation by North Las Vegas. Spring Valley west of the Strip became a town in 1981. Enterprise was formed in 1996 to stave off annexation by Henderson.
The Census Bureau recognizes the unincorporated towns as proper population divisions. The 2000 Census listed Paradise, with 186,070 residents at the time, as the most populated unincorporated town in the country. Sunrise Manor, with 156,120 people, and Spring Valley, with 117,390, were second and fifth on the list at the turn of the millennium.
