From Ancestry.com Wiki
Chelmsford is a town in Massachusetts. It was formed in 1655 and was previously called . It can be found in Middlesex county and is a part of the Northern registry of deed district. For more information, contact the county at 50 Billerica Rd., Chelmsford 01824. On the attached map, Chelmsford is shown as 12 in Middlesex county.
For information about the state of Massachusetts see Massachusetts Family History Research.