Armagh is a borough in Indiana County in the U.S. state of Pennsylvania. The population was 131 at the 2000 census.
Armagh is the oldest non-Indian community in Indiana County, having been founded in 1792 by eight families led by James and Margaret Jane Graham from the area now known as Northern Ireland. The community was named after the Irish city and county of Armagh, which was the hometown of some of the settlers. Its first school began in 1799, using a log cabin, and in 1805, it established the county's first post office.
The community became a borough on April 10, 1824, having previously been part of East Wheatfield Township.