WASHINGTON — Great Falls, Virginia; McLean, Virginia; and Potomac, Maryland, all make the top 50 on Bloomberg’s annual list of the wealthiest towns in the U.S., although all three slipped in their rankings from last year.

Bloomberg’s Richest Places list is based on average household income ranks in communities with at least 2,000 households based on average household income.

Great Falls ranks No. 16, down from 14th on last year’s list, with an average household income of $309,599.

McLean is No. 25, down from No. 20 last year, with an average household income of $283,922.

Potomac is No. 50, down from No. 46 last year, with an average household income of $248,189.

Bloomberg says wealth nationwide is concentrated in just six counties: Westchester County, New York; Bergen County, New Jersey; and Fairfield County, Connecticut — all New York City suburbs — as well as Cook County, Illinois; Los Angeles County, California; and Montgomery County, Maryland.

More than half of the 100 richest places in America are either in the New York City area or California.

The wealthiest community in the U.S. on Bloomberg’s list is Atherton, California, a Silicon Valley suburb whose residents include billionaires Eric Schmidt of Google and Sheryl Sandberg of Facebook. The average household income in Atherton is $450,696.

Rounding out the five wealthiest communities are Scarsdale, New York ($417,335); the Denver suburb of Cherry Hills Village, Colorado ($394,259); Los Altos Hill, California ($386,174), and Hillsborough, California ($373,128).