The War on Christmas is real, y'all. (Just kidding, it's still not a real thing.)
If you hail from the Midwest, you're most likely to feel the burning, hateful stare of a little old lady furious that you've wished her a holiday greeting other than "Merry Christmas." The Southern United States on the other hand, prefers "Happy Holidays." According to FiveThirtyEight, 20% of the South's respondents are African American, who show a strong preference for the secular greeting.
Religion and politics also come into play in this national data, with "republicans opposing “happy holidays” at the strongest rates and most consistently across the nation. Republican responses probably reflect opposition to political correctness as much as (and perhaps more so than) spiritual sympathies. Republicans as a whole (30 percent) outpace even evangelical Republicans (38 percent) in their anemic support for saying “happy holidays.” In other words, republicans have no chill.
Interestingly, areas known for being particularly non-religious, like Oregon, tend to prefer "Merry Christmas" because it's just not a big deal: "the social stakes are low — Christmas is not an entre to conversations about what church you attend, but more about presents, ugly sweaters and Santa." If you're strolling through Portland, you're less likely to start a battle in the War on Christmas with any kind of festive greeting than you are in a state with a large Christian population that's looking to defend their holy holiday.