Hollidaysburg is a borough in Blair County, Pennsylvania, on the Juniata River, 7 miles south of Altoona. It is the county seat of Blair County. It is part of the Altoona, Pennsylvania, Metropolitan Statistical Area and is one of the communities that comprises the Altoona Urban Area. In 1910, 3,734 lived there, and in 1940, 5,910 residents were counted. The population was 5,368 at the 2000 census. On the outskirts of Hollidaysburg are the Ant Hill Woods, famous for their colony of ants. 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. In 1900, 2,998 people lived in the borough. Hollidaysburg is located at 40° 25' 54"N 078° 23' 32"W / (40.431772, -78.392085).

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. (formerly James Industries, Inc.) More than a quarter billion Slinkys have been manufactured in the toy's history.

The center of Hollidaysburg is frequently referred to as "The Diamond," where the buildings and parking spaces form a diamond. This area serves as the hub for parades, festivals and other town celebrations.

The borough of Hollidaysburg was first laid out in 1796; by 1814 it consisted of several houses and a tavern. Hollidaysburg became the main transfer point between the Pennsylvania Canal and the Portage Railroad, a gateway to western Pennsylvania. The canal and Portage Railroad spurred industrial and commercial development in Hollidaysburg in the 1830s. In 1836, Hollidaysburg was established as a borough.

When Blair County was organized in 1846, the Borough of Hollidaysburg was designated the county seat. This designation allowed the borough to prosper when politicians and attorneys became attracted to the borough.

In 1903, the Pennsylvania Railroad constructed a large switching yard and US Route 22 was directed through the borough.