https://en.wikipedia.org/wiki/Las_Vegas_(TV_series)#Location

Setting
The location of the fictional Montecito has changed from season to season. Some of the first episodes were shot at the Monte Carlo and Mandalay Bay. Because of its similarity to Mandalay Bay, many of the show's visuals place the Montecito at the far southern end of the Las Vegas Strip, albeit usually across the street from Luxor on the airport side of Las Vegas Boulevard. The exact location and rotation of the building seems to vary within this area; indeed, the CGI zoom shots of the building's exterior in the season-two episode, "Montecito Lancers", shows the building in three slightly differing locations for three different shots. Also, a few interior and exterior shots were filmed in Dana Point, California, at the St. Regis Hotel in Monarch Beach. In season five, the Montecito seems to have a consistent location across from the Luxor.

Many of Mandalay Bay's interiors and exteriors (including its wave pool) have been used as Montecito exteriors, although (according to the Internet Movie Database) the actual set of Montecito is located at Culver Studios, in Culver City, California, so the interiors are a replica of the Mandalay Bay. The season-three set of Las Vegas has been said to be the biggest set for a TV show ever.

During the first season of the show, many of the Montecito's suites overlooked various parts of the middle part of the Strip, placing the hotel near where The Venetian, Flamingo Las Vegas, or The Mirage are located, before the more consistent location at the southern end of the Strip was finalized.

During the first season, except for the pilot episode, the sets were built as needed for filming.

Some episodes were shot using interior and exterior shots of Green Valley Ranch, including a shot of the pool and spa area where, in one episode, Everlast holds a concert.

In season three, Ed Deline's office appears to be in the middle of the strip, overlooking Harrah's, Caesars Palace, The Mirage, and The Venetian, which puts the Montecito near where Treasure Island is located. This is inconsistent with the flyover shots of the Montecito, which would place Ed's office over two miles away. Closer examination of the window scene shows that The Mirage's marquee over their driveway has been edited to read "Montecito". In season 4, "Died in Plain Sight", a scene in Ed Deline's office shows again an overview of The Mirage and Caesars Palace. Again, it is a confirmation that Ed Deline's office would be where Treasure Island is located.

According to an episode that originally aired in December 2005, the Montecito is located about 1.5 miles from Wynn Las Vegas. This distance is in a straight line ("as the crow flies") as opposed to a reference to actual driving distance. This distance is inconsistent with long shots that place the Montecito near the airport, Luxor, and Mandalay Bay, but is in line with the season-three visual references noted above. Other episodes show aerial shots of the Montecito that make it appear to be situated at the corner of Giles St. and Reno Ave., about half a mile from Mandalay Bay and across from the Luxor.