Allterton was born in Plymouth, Massachusetts, sometime around 1630, the only son and younger of two children of Isaac Allerton, a tailor, and the second of his three wives, Fear Brewster Allerton. Allerton’s mother died in the mid-1630s, after which he lived and received his early education in the household of his maternal grandfather, William Brewster, who had immigrated to Massachusetts in the Mayflower along with Allerton’s father and his father’s first wife. Brewster was a learned and religious man who had been one of the leaders of the separatists long before the Pilgrims had left England and the Netherlands for North America.
Following Brewster’s death in 1644, Isaac Allerton moved to New Haven to join his father, who had remarried and become a merchant engaged in extensive commerce with several colonies, including New Netherland, the West Indies, and Virginia. Allerton graduated from Harvard College in 1650 and then returned to New Haven to work in his father’s business. He married a woman named Elizabeth, surname unknown, and they had one daughter and one son. Allerton’s wife and son died about 1655, and his father died early in 1659.
In about 1660 Allerton left his young daughter in New England and moved to Virginia, where he owned land that his father had acquired. Unlike many immigrants for whom marriage into an influential Virginia family was a vehicle to prosperity and power, Allerton was already a man of substance and culture before he married twice-widowed Elizabeth Willoughby Overzee Colclough in about 1662. They had at least three daughters and one son. Over the next twenty years Allerton acquired more than 5,000 additional acres of land along the Rappahannock River. In August 1662 he was commissioned a justice of the peace in Westmoreland County, and not long thereafter he became an officer in the county militia. Although he had been brought up by New England separatists, he easily embraced Virginia’s Anglican establishment. The loss of the parish records makes it impossible to know whether he served on his local vestry, but in his will he left £10 to ornament the Cople Parish Church.
Allerton steadily ascended the military and civil ranks. Although surviving records reveal periods when he was an absentee officeholder, he was often exceptionally active in public life. If consistency of effort is a reliable measure, he was most committed to his work in the General Assembly. He represented Westmoreland County in the House of Burgesses in 1667, from 1680 to 1682, and in 1684, and sat for Northumberland County from 1668 to 1674 and 1676 to 1677. He was a leading man of business from the beginning and usually served on or chaired the main standing and ad hoc committees. He often conferred with the governor and Council, and he reported to the House on a range of critical issues, including the revenue bill of 1680, apportionment of the levy, the appellate jurisdiction of the burgesses, Indian affairs, the creation of towns, and the records of the House. Allerton was nominated for Speaker in 1680 but was not elected. Instead, he became chairman of the powerful Committee of Propositions and Grievances.
In August 1675 Governor Sir William Berkeley and the Council appointed Allerton, then a militia major, second in command to Colonel John Washington in a contingent cooperating with Maryland militiamen to protect the northern frontier from Indian attacks. Soon after the Virginians joined the Marylanders, five Susquehannock Indian leaders came out of their stronghold to confer and were killed at the direction of the Maryland commander. The complicity of the Virginia commanders was at worst passive. An eyewitness later testified that Allerton had objected to the executions, and in June 1677 a formal inquiry exonerated him.
The incident inflamed a crisis that in turn fueled Bacon’s Rebellion. Allerton served in the dramatic June 1676 session of the General Assembly before which Bacon’s men appeared in arms. Allerton remained loyal to Berkeley during the rebellion and was one of twenty men whom Nathaniel Bacon (1647–1676) denounced by name for sustaining Berkeley. After the rebellion Allerton moved from loyalty to Berkeley to support for the new regime of Governor Thomas Culpeper, second baron Culpeper of Thoresway. Not everyone made that transition, but Allerton’s contemporaries evidently did not fault him for continuing to support the government of the colony. He was one of the men who attempted to settle the complicated estate claim of the widow of a leading member of the rebellion, Giles Bland. Culpeper promoted Allerton to lieutenant colonel in 1680 and named him escheator of one or more of the counties in the Rappahannock River valley.
Culpeper also recommended Allerton for appointment to the Council. Charles II and James II both approved, but the Council had no vacancy until early in 1687. Allerton was sworn in as a councillor on April 21, 1687. Surviving records confirm his attendance at only eight of twenty-five sessions held during his tenure of exactly four years. On April 26, 1689, the governor and Council proclaimed William and Mary the monarchs of England and ordered a day of celebration. Allerton was present when the Council issued the order, but in April 1691, after Parliament required that the members of the Council take new oaths of allegiance, he and two other members relinquished their seats when they refused “thro Scruple of Conscience,” believing that their oaths to James II still bound them.
Allerton served one more term in the House of Burgesses. He represented Westmoreland County in the session of September 1696 and again served as chairman of the Committee of Propositions and Grievances. In October 1697 he wrote the burgesses that illness prevented him from attending the session of the assembly that had just begun, and with this notification he concluded a twenty-five-year career in the colony’s government. In the summer of 1699 the Council appointed him naval officer and receiver of Virginia duties in Westmoreland County, but he probably hired a deputy to perform most of the work.
Allerton wrote his will and dated it on October 25, 1702. He provided for his children and grandchildren in Virginia as well as the children of his first daughter, who had remained in New England. Allerton died between then and December 30, 1702, when his will was proved in the Westmoreland County Court.