“It was common for Scots-Irish extended families and even large segments of clans to settle in the same region. In Catawba County, North Carolina, over 300 Alexander families were identified in the first census of the United States in 1790.”
-- From “Southern Culture: An Introduction” by John Beck, Wendy Jean Frandsen and Aaron Randall (2009)
Update puzzler: I notice belatedly that Catawba County wasn’t created from Lincoln County until 1842.
One possible explanation: Mecklenburg County not only dates to 1762, but also included Hezekiah and numerous other Alexanders among its early residents. Even today among U.S. cities Charlotte is second only to Brooklyn (!) in Alexanders per capita.