Historically, the County was formed in March 1880 from portions of Washington and Allegheny Counties. In the mid 1800,s a portion of north Beaver County was incorporated to form part of what is now Lawrence County.

A law was passed in 1792 that opened the territory north and west of the Ohio River to occupancy by settlers, but hostilities with the Native Americans limited settlement until General Wayne's Treaty of Greenville in 1795.

Located within the boundaries of the future Beaver County was Logstown, situated on the Ohio River and a busy center of the Indian trade with the French and English in the mid - 1700's. Logstown was also the original site of the Harmony Society's village of Economy. George Washington visited this area at various times to survey the French forts and the general Ohio River area.

The townships and boroughs in Beaver County have changed frequently in the county's early years. Beaver County originally had six townships, split by the Ohio River. These townships were Sewickley, South Beaver and North Beaver Townships in the north half of the county, and Hanover, First Moon and Second Moon Townships south of the Ohio River. In 1814 the southern townships were reorganized into four approximately equal quarters and given the names Hopewell, Moon, Green and Hanover Townships. In 1816, the townships of Ohio and South Beaver were reorganized into four equivalent quarters: Ohio and Brighton Townships just north of the Ohio River, and South Beaver and Chippewa Townships further north.

The town of Beaver, located in Beaver Borough, is the County Seat. Beaver was chosen because it had already been laid out by surveyor Daniel Leet eight years before the establishment of the county. Beaver, Originally the site of Fort McIntosh, was considered a prime location for a town because of its location at the confluence of the Beaver and Ohio Rivers.