Its traditional county seat is Springfield,[1] the Connecticut River Valley's largest city, and economic and cultural capital; with an estimated population of 154,758, approximately one-third of Hampden County residents live in Springfield.

[2] Springfield grew at a pace far quicker than Northampton, so was granted shire town-status over its own southerly jurisdiction.

[2] The southern division of Hampshire County was separated as Hampden County on August 1, 1812, by a prior act of the Massachusetts General Court on February 25, 1812, with Springfield named as the shire town.

[3][4] The agreement of settlement (regarding assets, liabilities, income and expenses) made between Hampden and Hampshire counties in November 1812 can be found in the Court of Sessions Record Book 1, pages 5–6 of the Hampden County Commissioners' Archives, housed in the Registry of Deeds.

The Knowledge Corridor surrounding Springfield-Hartford is New England's second most populous urban area (after Greater Boston) with 1.9 million people.

As of the 2010 United States census, there were 463,490 people, 179,927 households, and 115,961 families residing in the county.

[22] The Hampden County Bar Association provides support and resources to the legal community and those seeking such representation.

[23] In part a legacy of the Eastern States Exposition, the Hampden County Improvement League, and Hampden County Beekeepers Association, both provide agricultural education and outreach.