( or ) is a town in Middlesex County, Massachusetts, United States. The population was 38,981 at the 2000 census.
Billerica's prehistoric history, represented by a Native American burial site, dates to circa 1000 B.C.
In the early 1630s a Praying Indian village named Shawsheen was at the current site of Billerica.
In 1638, Massachusetts Bay Governor John Winthrop and Lt. Governor Thomas Dudley were granted land along the Concord River in the wilderness which was called Shawshin by the local Native Americans. (Today, Shawshin is commonly spelled Shawsheen; see Shawsheen River.) Most of the settlement was to take place under the supervision of Cambridge; however, financial difficulties in the colony prevented this from taking place, and the issue of settling Shawshin continued to be deferred. Finally, in 1652, roughly a dozen families from Cambridge and Charlestown Village, later Woburn, had begun to occupy Shawshin as well.
Wishing to replace the foreign-sounding Shawshin with a name more familiar, the settlers chose the name Billerica, likely due to the fact that the majority of the families living in the settlement were originally from the town of Billericay in Essex, England. The town was incorporated as Billerica in 1655, on the same day as nearby Chelmsford and Groton. The oldest remaining homestead in the town is the Manning Manse, built in 1696, and later the residence of William Manning (1747–1814), the author of "The Key of Libberty," a critique of Federalist policies. (The unusual spelling of liberty is Manning's own.) Other notable Revolutionary War era residents included Asa Pollard (1735–1775), the first soldier killed at the Battle of Bunker Hill, and Thomas Ditson (born 1741), who was tarred and feathered by the British in 1775 while on a visit to Boston. The song "Yankee Doodle" supposedly became a term of national pride instead of an insult due to this event . The town now celebrates "Yankee Doodle Weekend" every September.