Brewer is the sister city of Bangor. The two are at the head of navigation on opposite sides of the Penobscot River estuary and are connected by three bridges. Brewer and Bangor were originally both part of Condeskeag Plantation, though the Brewer part was also called "New Worcester" after John Brewer's birthplace. In 1788 Orrington, Maine was incorporated with Brewer/New Worcester as its major village. The other half of Condeskeag incorporated in 1791 as Bangor. Finally, in 1812 Brewer broke away from Orrington and incorporated as a separate town.
According to the United States Census Bureau, the city has a total area of 15.68 square miles (40.61 km2), of which, 15.23 square miles (39.45 km2) is land and 0.45 square miles (1.17 km2) is water.
The villages of South Brewer and North Brewer are both within city limits. South Brewer was formerly the city's major industrial area.
This climatic region is typified by large seasonal temperature differences, with warm to hot (and often humid) summers and cold (sometimes severely cold) winters. According to the Köppen Climate Classification system, Brewer has a humid continental climate, abbreviated "Dfb" on climate maps.
The Victorian-style Daniel Sargent House (1847 and later) in South Brewer is listed on the National Register of Historic Places. Sargent was the owner of a large South Brewer sawmill. During the Civil War, he commanded the company of "Tigers" (Penobscot River Drivers) in the 2nd Maine Volunteer Infantry Regiment, also called "The Bangor Regiment". This was the first unit to march out of the state in 1861, and participated in 11 battles over two years. Sargent was eventually promoted to Lt. Col., or second in-command of the regiment.