A comparison of the results of the American Religious Identification Survey from 2008 with the results in 1990 (limited to the continental U.S.) shows that the nation has gone from being 86% self-identified as Christian in 1990 to 76% in 2008, a drop of twelve percentage points.
In some places, particularly in New England and the Northwest, the percentage identifying as Christian has grown particularly low as of 2008 (1990 figures in parenthesis):
Vermont 55% (84%) -29
Massachusetts 61% (83%) -22
New Hampshire 62% (85%) -23
Nevada 64% (80%) -16
Washington 64% (79%) -15
Oregon 66% (77%) -12
Wyoming 67% (84%) -17
Maine 69% (85%) -16
Idaho 69% (84%) -15
Montana 70% (86%) -16
Rhode Island 74% (88%) -14
Connecticut 74% (86%) -12
Every state in New England and the Northwest was more than three-quarters Christian and in all but a couple of cases more than four-fifths Christian in 1990. In 2008, that had dropped to less than three-quarters in every state and less that two-thirds in many of those states. Vermont, the least Christian state in the nation, is just 55% Christian.
The Sharp Slide in Roman Catholic Identification
A significant part of the change in New England is attributable to the demise of white Catholicism. Consider the percentage of Catholic in each of the New England States (versus 1990):
Massachusetts 34% (54%) -20
Connecticut 38% (50%) -12
Vermont 26% (37%) -11
New Hampshire 32% (41%) -9
Rhode Island 46% (62%) -16
Maine 22% (31%) -9
In 1990, half the adults in three New England states identified as Catholics. Now, there is no U.S. state where a majority of adults identify as Catholic. Every New England State has seen a drop of at least at least a fifth in the population share that is Catholic, and the drop has been more than 30% in some states.
Among non-Hispanic whites, 27% identified as Catholic in 1990, while 21% did in 2008, a drop in more than a fifth in share of the total non-Hispanic white population. Among non-Hispanic blacks, 9% identified as Catholic in 1990, while 6% did in 2008, a drop of a third in share of total non-Hispanic black population. Among Hispanics, 66% identified as Catholic in 1990 compared to 59% in 2008, a drop of about ten percent in overall share. Among Asian-Americans the percentage identifying as Catholic was 27% in 1990 compared to 17% in 2008, a drop of more than a third in overall share.
In every racial and ethnic category, the decline in the percentage of the population identifying as Roman Catholic has been very close to the rise in the percentage of the population identifying as non-religious. Obviously, the reality is more complicated. Many people who formerly identified as Roman Catholics now identify with some other branch of Christianity or as "Christian" generally. Many people who identified as Christians of some non-Catholic faith now consider themselves to be non-religious.
A surge in the percentage of the population that is Hispanic, a population that is much more likely to be Roman Catholic than the United States as a whole, as concealed slippage in Roman Catholicism among all ethnic groups in the United States.
The percentage of people identifying with some non-Catholic form of Christianity has been more stable for non-Hispanic Whites, for Blacks and for Hispanics, but there has been a dramatic drop in the share of Asian-Americans who identify with any form of Christianity, mostly due to growth in the share of the Asian-American population that identifies as Muslim or affiliated with an Eastern Religion, in significant part due to immigration of non-Christians from South Asia ad East Asia.