[1] As of the 2020 census, the population was 152,199,[2] making it the third-most-populous county in Maine.

Penobscot County comprises the Bangor, ME Metropolitan Statistical Area.

[4] The county highpoint is East Turner Mountain at 2,456 feet (749 m) next to Baxter State Park.

At the 2000 census there were 144,919 people, 58,096 households, and 37,820 families living in the county.

At the 2010 census, there were 153,923 people, 62,966 households, and 38,917 families living in the county.

[12] In terms of ancestry, 20.9% were English, 17.2% were Irish, 9.4% were American, 7.1% were German, 6.0% were French Canadian, and 5.9% were Scottish.

[15] As the most populous county in Maine's 2nd congressional district, Penobscot County's support for Donald Trump in 2016 helped deliver him a split electoral vote from Maine.

School districts include:[19] University of Maine is in Orono.