[3] Prior to European contact, this area was settled for thousands of years by succeeding cultures of indigenous peoples.

During the colonial era, historic native groups known by the colonists to settle in the area included members of western nations of the Iroquois, such as the Seneca; the Lenape, who had been pushed from the East by European-American settlers; the Shawnee, who also had territory in Ohio; and the Mingo, a group made up of a variety of peoples from more eastern tribes.

European fur traders such as Peter Chartier established trading posts in the region in the early eighteenth century.

In 1749, Captain Pierre Joseph Céloron de Blainville claimed the Ohio Valley and all of western Pennsylvania for King Louis XV of France.

Most of the towns during that era were developed along waterways, which were the primary transportation routes, as well as providing water for domestic uses.

Through the eighteenth century, both the French and the British competed for control over the local rivers in this frontier territory of North America.

Native American bands and tribes allied with the colonists to differing degrees, often based on their trading relationships.

Given its strategic location at the Ohio, Fort Duquesne became an important focal point of the French and Indian War.

It was formed to respond to pressure from the increase in settlers living in the area around Pittsburgh; this was designated as the county seat in 1791.

The county originally extended north to the shores of Lake Erie; it was reduced to its current borders by 1800.

Although the county's industrial growth resulted in clearcutting of the area's forests, a significant amount of woodland has regrown.

The county government was charged with all local activities, including elections, prisons, airports, public health, and city planning.

The changes were intended to maintain a separation of powers between the executive and legislative branches while providing greater citizen control.

[17] The legislative branch consists of the County Council, which is composed of 15 members elected for four-year terms from 13 single-member districts and 2 At-Large representatives, currently occupied by Bethany Hallam and Sam DeMarco.

These include one city (Pittsburgh), 96 boroughs, 30 townships, and two home rule municipalities (Bethel Park and McCandless).

[21] There have been several proposals to consolidate or merge some of the municipalities in Allegheny County, either with each other or with the City of Pittsburgh, to reduce costs, improve efficiency, and enhance regional cooperation.

[22][23] One of the most recent proposals is from Wilkinsburg, a borough that borders Pittsburgh and faces financial challenges due to declining population and tax base.

[22] Another recent proposal is from Allegheny County Economic Development (ACED), which is seeking to enter into an agreement with a consultant to carry out historic preservation compliance activities for projects funded by various federal programs.

ACED issued a Request for Proposals (RFP) for this service in January 2022 and expects to select a consultant by March 2022.

Since the Great Depression on the state and national levels, the Democratic Party has been dominant in county-level politics.

In 2006, Democrats Governor Ed Rendell and Senator Bob Casey Jr. won 59% and 65% of the vote in Allegheny County, respectively.

In 2008, Democrat Barack Obama received 57% of the vote, Republican John McCain received 41%, and each of the three state row office winners (Rob McCord for Treasurer, Jack Wagner for Auditor General, and Tom Corbett for Attorney General) also carried Allegheny.

In the 21st century, populist turns to the GOP from nearly all of Appalachia in general and western Pennsylvania in particular have left the county as one of the few in the region that still supports the Democrats at a high level.

Coupled with deposits of iron and coal, and the easy access to waterways for barge traffic, the city quickly became one of the most important steel producing areas in the world.

Based on 2007 data from the US Army Corps of Engineers, Pittsburgh is the second (after Laredo, Texas) busiest inland port in the nation.

US steel production declined late in the 20th century, and Allegheny County's economy began a shift to other industries.

Despite the decline of heavy industry, Pittsburgh is home to a number of major companies and is ranked in the top ten among US cities hosting headquarters of Fortune 500 corporations, including U.S. Steel Corporation, PNC Financial Services Group, PPG Industries, and H. J. Heinz Company.

Pennsylvania State Game Lands Number 203 is also located in Allegheny County providing hunting and other activities.

[48]Under Pennsylvania law, there are four types of incorporated municipalities: cities, boroughs, townships, and (in a case) a town.

The following municipalities are in Allegheny County: Census-designated places are geographical areas designated by the US Census Bureau for the purposes of compiling demographic data.