This Silicon Valley enclave is once again America's most expensive zip code

Atherton, a small town in Silicon Valley, has been named America's most expensive zip code for the third year in a row, according to Forbes.

To determine the rankings, Mountain View-based firm Altos Research calculated the median home listing prices for 28,500 zip codes across the country. Co-ops were excluded, and calculations were adjusted based on the makeup of the housing stock in each particular market.

In Atherton, the median listing price was a whopping $10.6 million, landing it at the top of the list. The median listing price was $9.03 million at the time Forbes compiled its list for 2014.

The town itself is quiet and secluded, and building codes prohibit commercial development. Still, it's not far from the bustling tech-centric towns of Palo Alto and Menlo Park.

Several noted tech billionaires, including Microsoft cofounder Paul Allen, Google chairman Eric Schmidt, and HP CEO Meg Whitman, currently own homes here. Facebook COO Sheryl Sandberg also lived in Atherton before she moved into her new waterfall-equipped home in nearby Menlo Park in 2013.

Here are the top 10 zip codes on Forbes' list:

1. Atherton, California (94027) - $10.6 million

2. Sagaponack, New York (11962) - $7.4 million

3. New York, New York (10012) - $7.3 million

4. Woody Creek, Colorado (81656) - $7 million

5. New York, New York (10013) - $6.1 million

6. Miami Beach, Florida (33109) - $5.6 million

7. Woodside, California (94062) - $5.5 million

8. Hidden Hills, California (91302) - $5.1 million

9. Aspen, Colorado (81611) - $5 million

10. Hillsborough, California (94010) - $4.9 million