The Barna Research Group, an evangelical Christian organization that does surveys and research to better understand what Christians believe and how they behave, studied divorce rates in America in 1999 and found surprising evidence that divorce is far lower among atheists than among conservative Christians.
The highest divorce rates are in the Bible Belt: "Tennessee, Arkansas, Alabama and Oklahoma round out the Top Five in frequency of divorce...the divorce rates in these conservative states are roughly 50 percent above the national average" of 4.2/1000 people. Nine states in the Northeast (Connecticut, Maine, New Hampshire, New York, Pennsylvania, Vermont, Rhode Island, New Jersey, and Maryland) have the lowest divorce rates, averaging just 3.5/1000 people.
Barna isn't the only group to arrive at these numbers. Other researchers have also found that conservative Protestants get divorced more often than other groups, even more often than "mainline" Protestants. The fact that atheists and agnostics divorce less often than other religious groups was, however, surprising to many.
The difference in divorce rates is particularly interesting given the fact that the Christians getting divorced in the highest numbers are among the same Christians who are most likely to raise an alarm about the state of marriage in society. They also tend to be the same Christians who want to deny gays the right to marry on the assumption that gay marriage is a "threat" to the institution of marriage. If marriage is in any danger in America, perhaps the threat comes from the unstable marriages of conservative Christians, not the relationships of gays or the marriages of godless atheists.