Do you need to be rich to get elected to Congress? Or does getting elected to Congress make you rich?
Whatever the cause and effect, Congress is now officially the land of millionaires.
According to the Center for Responsive Politics, a majority—268 of the 534 members of Congress—had an average net worth in 2012 of $1 million or more, marking the first time millionaires held a majority in Congress.
The previous year, only 257 members had millionaire status.
The median net worth for the lawmakers who were in Congress as of the May 2013 filing was $1,008,767, up from the previous year's $966,000.
(Read more: Millionaires placing their bets on Europe)
Of course Congress—and especially the Senate—has long been a wealthy club. But millionaires have always been in the minority. The Center for Responsive Politics said that this is a "watershed" moment and shows how removed Congress has become from the concerns of most, nonmillionaire Americans.
"Despite the fact that polls show how dissatisfied Americans are with Congress overall, there's been no change in our appetite to elect affluent politicians to represent our concerns in Washington," said Sheila Krumholz, executive director of the center. "Of course, it's undeniable that in our electoral system, candidates need access to wealth to run financially viable campaigns, and the most successful fundraisers are politicians who swim in those circles to begin with."
(Read more: QE: The greatest subsidy to the rich ever?)
For all of Congress, Democrats are richer than Republicans. Congressional Democrats had a median net worth of $1.04 million, while congressional Republicans had a median net worth of almost exactly $1 million. In both cases, the figures are up from the previous year, when the numbers were $990,000 and $907,000, respectively.
The Senate is much richer than the House. The median net worth for all senators increased to $2.7 million from $2.5 million. In the Senate, Republicans are richer than Democrats. Senate Democrats reported a median net worth of $1.7 million (a decline from 2011's $2.4 million), compared with Senate Republicans, at $2.9 million (an increase from $2.5 million).
—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.