Blair County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 122,822. Its county seat is Hollidaysburg. The county was created on February 26, 1846, from parts of Huntingdon and Bedford counties. Blair County comprises the Altoona, PA metropolitan statistical area. It is also part of the Altoona-Huntingdon, PA Combined Statistical Area, which includes Blair and Huntingdon counties.