[6] Mifflin County is located in, and has its boundaries defined by, the Ridge-and Valley Appalachian Mountains of Pennsylvania.

The county is one of the 423 counties served by the Appalachian Regional Commission,[7] and it is identified as part of the "Midlands" by Colin Woodard in his book American Nations: A History of the Eleven Rival Regional Cultures of North America.

The county has a humid continental climate (Dfa/Dfb) and average temperatures in downtown Lewistown range from 27.8 °F in January to 72.7 °F in July.

Few non-Amish or Mennonites in Mifflin County today speak Pennsylvania German, but this was not true in the past.

The United States Office of Management and Budget[19] has designated Mifflin County as the Lewistown, PA Micropolitan Statistical Area (μSA).

Head Start is a federally and state funded preschool program for low income children.

(Closed 2019) The Penn State Learning Center in Lewistown offers both two-year and four-year degrees.

Recently, the Learning Center opened a state-of-the-art science lab to be used by students attending the Lewistown Hospital School of Nursing.

Mifflin County does not have a local television station but it is provided with local coverage from the following stations outside of the county from both the Harrisburg and Johnstown/Altoona markets: Under Pennsylvania law, there are four types of incorporated municipalities: cities, boroughs, townships, and, in at most two cases, towns.

Census-designated places are geographical areas designated by the US Census Bureau for the purpose of compiling demographic data.