This is the most expensive zip code in the US — and it's not in California or New York

Joe Raedle | Getty Images

Areas like Silicon Valley and Beverly Hills, California attract the West Coast wealthy and Manhattan lures East Coast elites. But the richest zip code in the United States actually belongs to a little island in Florida, according to a new Bloomberg study.

Located just minutes off the coast of Miami, Fisher Island (zip code 33109) has some wealthy residents, with the average income there a whopping $2.5 million in 2015, according to a Bloomberg analysis of 2015 Internal Revenue Service data.

The private, man-made island, was once home to the winter estate of railroad fortune heir William K. Vanderbilt, according to the Fisher Island Club, the island's centerpiece resort. Now, his Vanderbilt Mansion sits at the crux of the club's facilities.

A look at the Vanderbilt Mansion on Fisher Island, Florida
Getty Images | Michelle Kanaar/Miami Herald/MCT

Only accessible by yacht or private ferry, the island has an observatory, a 24,000-square foot spa, a lush golf course, a private beach with butler service and an aviary featuring over a dozen exotic birds, among other amenities. Golf carts are the main mode of transportation on Fisher.

Belonging to Fisher Island Club, which is available to non-property owners, isn't cheap. Annual memberships have a one-time fee of $42,800 and yearly dues of $27,734. Equity membership for Fisher Island property owners requires a $250,000 buy in, along with annual dues of $20,651.

Marka | Getty Images

Over 650 families from 42 countries live on Fisher Island, according to the club, although less than 20 percent of them live there year-round. The island has reportedly attracted celebrities like Oprah Winfrey.

On, the most expensive listing on Fisher Island is a four-bedroom, 6,644- square-foot residence with a $26,411,500 asking price. The least expensive is a one-bedroom condo for $975,000.

Peter Bischoff | Getty Images

Looking to visit the 216-acre island? The luxurious Fisher Island Club Hotel offers several villas, guest house suites and cottages. For a two-night stay in early August, rates range from a little under $800 a night to $3,000.

After Fisher Island, taking second place in Bloomberg's ranking with an average income of slightly less than $1.5 million in 2015, is Atherton, California, located in Silicon Valley. In third is Palm Beach, Florida, the county in which President Donald Trump's massive, Mar-a-Lago estate is located. The enclave has an average income of over $1.2 million, according to Bloomberg. Other highly-coveted zip codes on the list include Palo Alto, California (ranked fourth), San Francisco (ranked 10th) and Naples, Florida (ranked 15th).

To determine its ranking, Bloomberg evaluated IRS data for zip codes with over 200 tax returns as of the 2015 filing season and with 500 residential households, according to the latest Census tally.

Don't miss: Donald Trump used to own this $45 million Connecticut mansion with Ivana — take a look inside

Where to find the best luxury real estate buys in the world
Where to find the best luxury real estate buys in the world