The "Evil Empire," as Boston Red Sox president Larry Lucchino once called the New York Yankees, occupies territory far beyond the Bronx. Virginia, North Carolina, Louisiana, New Mexico—according to Facebook, all are Yankee country.

With the baseball season beginning in earnest on Monday, Facebook examined which of the 30 teams are most popular in each county nationwide, by Facebook likes of their team pages. Most teams win only in their respective geographic regions, but not the Yankees, who also are the preferred...