At least 268 of the 534 politicians in the Senate and House of Representatives had a net worth of m (£606,821) or more in 2012.
Democrats were slightly wealthier than Republicans, found the data from the Center for Responsive Politics (CRP) at OpenSecrets.org.
It comes as politicians debate national jobless benefits and the minimum wage.
Democrats registered a median wealth of .04m while Republicans had m.
Senators ranked higher than members of the House in median wealth, with .7m versus 96,000 in the lower chamber.
The wealthiest member of Congress was Republican Congressman Darrell Issa. The Californian reported a net worth of up to 98m, earned largely through sales of a car antitheft system.
The poorest member of Congress was also a California Republican, Congressman David Valadao. He listed debts upwards of 2m, largely stemming from loans on a family dairy farm.
As Congress suffers under some of its lowest approval ratings in history, “there’s been no change in our appetite to elect affluent politicians to represent our concerns in Washington”, CRP director Sheila Krumholz told the Agence France-Presse news agency.
Also necessary is wealth “to run financially viable campaigns”, she added.
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