Killingly is the largest town by population in the Northeastern Connecticut Planning Region.

It was first called "Aspinock", a word which may have come from the combination of the native term "aucks" or "ock" (the place of/where) and the name of the English settler, Lieutenant Aspinwall.

Saltonstall's ancestral manorial possessions lay in Killanslie and Pontefract, Yorkshire, hence he suggested “Kellingly” (the spelling was later altered).

The borough of Danielson and the town of Killingly contain a small Laotian community.

Both are on the nation's list of top 50 cities with the highest percentage of citizens claiming Laotian ancestry.

[9] Bus service to the area is provided by the Northeastern Connecticut Transit District.