412 is the telephone area code for much of Allegheny County, though it covered much more geographically at the time the name was coined, prior to the introduction of 724. Both 412 and 724 are now part of an overlay complex in which the entire region served by those codes is also covered by 878.
^O'Brien, Jim; Marty Wolfson (1980). Pittsburgh, the story of the city of champions: the '70s—a decade unmatched in the annals of sports. Wolfson Pub. Co. ISBN 978-0-916114-07-7.
^Scarpaci, Joseph L; Kevin Joseph Patrick (2006). "Chapter 6: Pittsburgh, City of Bridges". Pittsburgh and the Appalachians: cultural and natural resources in a postindustrial age. Pittsburgh: University of Pittsburgh Press. p. 81. ISBN 978-0-8229-4282-5. Retrieved February 28, 2010.
^Rossi, Rob (February 14, 2010). "Deadline-day deal? Not likely for Penguins". Pittsburgh Tribune-Review. Archived from the original on September 10, 2012. Retrieved February 28, 2010.
^Bobkoff, Dan (December 16, 2010). "From Steel To Tech, Pittsburgh Transforms Itself". NPR. Retrieved December 21, 2010.