[a] In the Treaty of Fort Stanwix of 1768, new lands in Pennsylvania were purchased from the Haudenosaunee for colonial settlement, including parts of what is now Clinton County.

The land was formally associated with Northumberland County, but a group of organized settlers near modern Jersey Shore elected three commissioners each March who were responsible for seeing that everyone was dealt with fairly.

[6] The county has a humid continental climate which is warm-summer (Dfb) except in lower areas near the West Branch and the Bald Eagle Creek which are hot-summer (Dfa).

The United States Office of Management and Budget[12] has designated Clinton County as the Lock Haven, PA Micropolitan Statistical Area (μSA).

While Clinton County has historically been Republican like the rest of central Pennsylvania, Democrats captured the registration edge in early 2008.

This was followed in 2010 with U.S. Senate candidate, Republican Pat Toomey, receiving 59% to 41% for Democrat Joe Sestak.

In 2012, Mitt Romney carried the county 55% to President Obama's 43%, while incumbent Democratic Senator Bob Casey, Jr. received 44% to his Republican challenger, Tom Smith's 53%.

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 Clinton County: Census-designated places are unincorporated communities designated by the U.S. Census Bureau for the purposes of compiling demographic data.