Hollidaysburg is a borough and the county seat of Blair County in the U.S. state of Pennsylvania. It is located on the Juniata River, 5 miles south of Altoona and is part of the Altoona, Pennsylvania, Metropolitan Statistical Area. In 1900, 2,998 people lived in the borough, in 1910, 3,734 lived there, and in 1940, 5,910 residents were counted. The population was 5,791 at the 2010 census. Coal, iron ore, ganister, and limestone are found in the vicinity. In the past, the borough had foundries and machine shops, a silk mill, car works and classification yards.From 1834 to 1854, the borough was an important port on Pennsylvania Main Line Canal, where the Juniata Division Canal connected to the Allegheny Portage Railroad.The famous toy known as the Slinky is manufactured within Hollidaysburg by Poof-Slinky, Inc.. More than a quarter billion Slinkys have been manufactured in the toy's history.