Thomas was the son of Sir Richard Caswell and Mary Slany.
He was an early resident of Taunton as in 1643 he was on a roster of the First Military Company of Taunton. This was a list of "all the males able to beare armes from XVI years to 60 yeares". He was most probably born in England, but it is not now known when he came to this country. He was probably not one of the original settlers of Taunton because he does not appear on the list of the 46 original purchasers or the list of 35 subsequent purchasers.
It is not known where in England Thomas came from but the Caswell name is common in the county of Somerset, and a large number of Somersetshire families settled in Taunton. In the parish of North Curry, Somerset on October 20, 1618, Thomas Caswell, son of Thomas Caswell, was baptized. This Thomas would be of the right age to be the Thomas of Taunton, but proof of a connection is lacking. Thomas probably married in Taunton about 1648 to Mary ______. Mary's maiden name is unknown, but her son Peter, in a testamentary deed, made mention of his "aunt Bryant". This could be Mary's sister, but unfortunately her maiden name cannot be established either.
In 1651 Thomas and eleven other townsmen made up a panel of inquest into the drowning death of a ten year old William England, servant to Joseph Wildbore, who accidentally fell out of a canoe on the Great River (now Taunton River). Thomas signed his name, "thos: Caswell", to the verdict. The people of Taunton chose Thomas as hayward on March 11, 1655, apparently the only elected position he ever held. In 1657 :"Tho: Casswell" took the Oath of Fidelity in taunton. In 1662 he served on the "Grand Enquest" for the Colony of New Plymouth. In 1667 he was again called upon to serve with eleven others on a panel of inquest into the accidental drowning of Timothy Poole, to which he signed his name "Thomas Caswell".
Thomas settled on the land that had belonged to John Kingsley, an original proprietor who had moved to Rehoboth, MA. On December 28, 1659 he was granted 42 acres of land in Taunton, and there were nine in his family at the time. He and his wife and six children account for eight. The ninth may have been a servant, a child whose birth and death were not recorded, or some other relative. On the sixth of June 1668 Thomas was one of those to purchase shares in the Taunton North Purchase, which was later set off as Norton, parts of Mansfield and Easton. Several years later he was also involved in the South Purchase, a four square mile tract bought from King Phillip and which now lies within the town of Berkley. Thomas was listed a head of household in 1675, a year in which King Phillip was apparently having second thoughts about his earlier land sale to the English.
Thomas Caswell's name appears on a rate list dated October 16, 1683 to defray the expenses of plastering the meeting house, his comparitively large assessment being one shilling eleven pence. He was also assessed eighteen shillings as his proportion of the sum to be paid to purchase Mr. Danforth's land, according to an undated Taunton list.
Also in 1683 the name of Thomas Caswelll was included on a military document, and, although this was probably Thomas Jr., an abstract is included here in order to give a flavor of the times. The Taunton Military Company was split at this time into four squadrons. The members of each squadron were to bring their fire arms to Sunday meeting once a month, each squadron taking a different sabbath. The court ordered that every soldier was to bring his arms when it was his turn with six charges of powder and shot and to be fined if he failed to do so. A steeper fine was to be imposed if he refused. Also, any member who stayed away from meeting because they would not bring their arms were to be summoned to court. Apparently the arms were necessary to protect the congregation against Indian attack. In the 1691 Inspection Return, taken at the time of King William's War, "Thomas Caswell, sen" is shown as having been supplied with a gun, a cartouch box, powder, and bullets, while the following year his gun was pressed for Nathan Presbiter and valued at oe1. In 1693 Thomas served on a jury ordered by the town to lay out a road to William Hack's the report of which he signed on May 27, 1693.
As for Thomas Caswell's land holdings, on November 27, 1649, at a town meeting, he was granted his second division, on the other side of Two Mile River opposite Thomas Coggins' land extending to the head of the great lots there. The wording of this grant seems to imply an earlier grant, possibly in the first division, but no record of this has been found. On December 28, 1659 he was granted forty-two acres for "9 heads" (mentioned above) on which he paid a tax of 11 shillings and three pence On January 3, 1660 it was said that Thomas Caswell's home lot shall extend in length as far as Shadrach Wildbore's land. The Proprietors' records list the land in possession of Thomas Caswell Sr. on Jan. 8, 1665 as follows: his home lot, 6 acres, lying between Samuel Wilbore to the east and the widow Paul on the southwest; the additon to his home lot, being on the other side of the Great River, between Samuel Wilbore on the southwest and Morris Farwell on the east; 4 acres of meadow on the other side of the Great River lying between two brooks, Walter Dean's meadow lying to the west of this tract on ther other side of one of the brooks; one pond, called the "Stage Pond" being three acres lying between the Iron Works and the Four Mill Pond (called Titicut Pond); his "division" being 11 acres at the east end of the above meadow, bounded by James Bell's land on the east end and the Great River on the northwest, and extending to the Common on the south; and his "second division" of land, being 42 acres lying on the southeast side of his meadow, with "Plymouth path" on the west and the land of widow Dean on the southeast, and extending to a little plain being a "common".
Later, on March 22, 1669, Thomas was granted three acres of swamp on the Three Mile River "at a place where the beavers did dam up the water". On October 24, 1682 he was further granted thirty acres on John Kingsley's right and on December 23, 1684 he was granted two acres at a place called Pool's Brook, the western bound of which was the path that came from the Iron Works.
Thomas' will was dated September 28, 1691 with a codicil dated March 15, 1696-7 and was probated September 14, 1697. In it he mentioned his wife Mary and his six sons and daughters. The inventory of the estate was taken March 30, 1697 and amounted to 306.09.06. On March 12, 1721-2 his son Thomas and daughters Mary Thrasher, Sarah Hoskins, Hannah Ramsdel, Elizabeth Leonard, Abigail Jones, and Esther Smith sold their rights in Thomas' estate to their brother Samuel.