The town is part of the Lower Connecticut River Valley Planning Region.

[2] Killingworth was established from the area called Hammonasset, taken from the local Native American tribe of the same name.

Abraham Pierson, the college's first president, taught some of the first classes in his Killingworth home—which is actually in present-day Clinton, Connecticut.

[5] According to the United States Census Bureau, the town has an area of 35.8 square miles (93 km2).

Students attending school in Killingworth are a part of Connecticut's Regional School District #17, which consists of Haddam and its villages of Haddam Neck (located on the eastern bank of the Connecticut River) and Higganum.

Services include connections to the Old Saybrook Train Station, served by Amtrak and Shoreline East railroads.

The town was the subject of the poet Henry Wadsworth Longfellow's poem "The Birds of Killingworth" published in Tales of a Wayside Inn.

1999: The largest tree in Rockefeller Center history, 100 feet (30 m) high, was chosen from Killingworth, CT.