“What might be called New South and Old South not only coexist, atypical in a region where rapid growth and the influx of outsiders have often fomented cultural clashes, but each appreciates the value the other brings to the table,” the local author Bob Burtman wrote in a 2010 anthology about the town.

Evelyn Poole-Kober, the vice chairwoman of the Orange County Republican Party, who stepped carefully through the glass shards of the blackened office Monday morning, said she had witnessed the cultural change since moving to the area in the early 1980s. She said she was long used to living among Democrats and was friendly with many of them, including members of her garden club.

Orange County, with Hillsborough as its seat, includes nearly all of liberal Chapel Hill, home to the University of North Carolina. Nearly half of the county’s approximately 116,000 voters are registered Democrats, and fewer than 15 percent of voters signed up as Republicans. A substantial number of voters — nearly 38 percent — are unaffiliated.

Ms. Poole-Kober said she could not imagine that a local person was responsible for the attack, given the friendly tenor of the town.

But she did not play down the seriousness.

She said Mr. Stevens approached her on Sunday and said, “Oh, this is sad, Evelyn.”

“I said, ‘No, it’s not sad — it’s evil,’” she recalled.

The Hillsborough police said someone had hurled “a bottle containing flammable material” through the front window of the headquarters. The authorities said they believed that the fire extinguished itself after burning furniture and causing “heavy smoke damage.”