According to Pew Research
The religious face of America is largely a Christian one, with roughly seven-in-ten Americans belonging to that faith. But some of the nation’s biggest metropolitan areas have a very different look.
Only about half of the residents in the Seattle (52%) and San Francisco (48%) metropolitan areas identify as Christians, as well as roughly six-in-ten or fewer of those living in Boston (57%) and New York (59%).
When Pew describes someone as “Christian,” they are reporting that the person identifies as “Christian” when asked what religion they are.
Here’s the religious affiliation of Americans state by state