[2] The county seat is Harrisburg,[3] Pennsylvania's state capital and ninth-most populous city.

[5] The county is bound to its western border by the Susquehanna River (with the exception of a small peninsula next to Duncannon).

Most of the county by area has a humid continental climate (Dfa except for some Dfb in highlands.)

The inclusion of temperature numbers for the past decade shows some lower-lying areas, including Harrisburg, to have a humid subtropical climate (Cfa.)

A study by Echelon Insights found Dauphin County to be the most typical county in America, with its 2016 presidential vote, median income, higher education rate, and religiosity all very close to the national averages.

The community was settled by Amish from Lancaster County seeking cheaper land.

[20] The United States Office of Management and Budget[21] has designated Dauphin County as the Harrisburg-Carlisle, PA Metropolitan Statistical Area (MSA).

It was long one of the more conservative urban counties in the nation, having only supported a Democrat for president twice from 1880 to 2004.

Bob Casey Jr. carried the county in the 2006 Senate election when he unseated Rick Santorum.

In 2023, with the election of newcomer Justin Douglas to join George Hartwick, III, the Democrats took a majority on the Board of County Commissioners for the first time in nearly 100 years.

As of July 29, 2024, 44.0% of registered voters in the county were Democrats, 38.6% Republicans, 13.3% non-affiliated, and 4.1% other party.

It is governed by a 17-member Board of Trustees, five appointed annually by the Dauphin County Commissioners, and twelve elected for three-year terms.

Under Pennsylvania law, there are four types of incorporated municipalities: cities, boroughs, townships, and, in at most two cases, towns.

The following cities, boroughs and townships are located in Dauphin County: Census-designated places are geographical areas designated by the U.S. Census Bureau for the purposes of compiling demographic data.