Penobscot County is the third largest in population of the sixteen Maine Counties. Located in eastern central Maine it is bisected by the Penobscot River and, Interstate 95.

Created on April 1, 1816 from the northern part of what was then all of Hancock County it later gave up territory to form Piscataquis and Aroostook counties. As with many counties, towns and borders changed throughout the early 19th century.

The county currently consists of the cities of Bangor, Brewer, Old Town; and towns of Alton, Bradford, Bradley, Burlington, Carmel, Charleston, Chester, Clifton, Corinna, Corinth, Dexter, Dixmont, East Millinocket, Eddington, Edinburg, Enfield, Etna, Exeter, Garland, Glenburn, Greenbush, Hampden, Hermon, Holden, Howland, Hudson, Kenduskeag, Lagrange, Lakeville, Lee, Levant, Lincoln, Lowell, Mattawamkeag, Maxfield, Medway, Milford, Millinocket, Mount Chase, Newburgh, Newport, Orono, Orrington, Passadumkeag, Patten, Plymouth, Springfield, Stacyville, Stetson, Veazie, Winn, Woodville; the plantations of Carroll, Drew, Seboeis, and Webster; townships including Argyle, Greenfield, Kingman, Mattamiscontis, among others;  and the Penobscot Nation reservation on Indian Island in the Penobscot River.

The City of Bangor is the County Seat, hosting the county government, courthouse, and the county jail.

In 2010, Penobscot County’s population represented 11.6% of the state’s total, with a census count of 153,923 a 6.2% increase over 2000, the largest percentage increase of any county and more than 50% greater than for the entire state.