Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Billerica is a town in Middlesex County, Massachusetts, United States. The population was 40,243 at the 2010 census. It is the only town named Billerica in the United States and borrows its name from the town of Billericay in Essex, England. 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.