Hollidaysburg is a borough in and the county seat of Blair County in the U.S. state of Pennsylvania. It is located on the Juniata River, 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.