The county is part of the South Central Pennsylvania region of the state.

[5] Franklin County is in the watershed of the Chesapeake Bay and the overwhelming majority of it is drained by the Potomac River, but the Conodoguinet Creek and the Shermans Creek drain northeastern portions into the Susquehanna River.

It has a hot-summer humid continental climate (Dfa) and its hardiness zone is 6b.

Average monthly temperatures in Chambersburg range from 29.9 °F in January to 74.7 °F in July.

As a testament to the county's status as a Republican Party stronghold, Jimmy Carter in 1976 is the lone Democrat to win forty percent of the county's votes since Johnson's 1964 win.

It runs Summer Academy, which offers both art and academic strands designed to meet the individual needs of gifted, talented and high achieving students.

Public school districts include:[16] The Franklin County Library system has five branches: The system also supports the Alexander Hamilton Memorial Library in Waynesboro, PA.

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

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

The population ranking of the following table is based on the 2010 census of Franklin County.