Cyrus Baldwin (1740-1790), the first child of James and Ruth Baldwin of Woburn, Massachusetts, was born on November 3, 1740. During the Revolutionary War, Cyrus settled in Boston as a merchant and also served as a 1st Lieutenant in Colonel Henry Bromfield's Boston militia regiment. Sometime following 1777, he moved to Dunstable, New Hampshire, where, again, he became a successful merchant. He served for a time as a representative to the New Hampshire State Legislature, but his political career was abruptly halted when he drowned in Dunstable two days after his fiftieth birthday, November 5, 1790. He was buried five days later in Woburn. He had been married to Ruth Wilson of Bedford, and he died without issue.

Loammi Baldwin (1745-1807) was born at New Bridge (North Woburn) on January 21, 1745, the second son of James and Ruth Baldwin. A bright and inquisitive child, Loammi studied under Master John Fowle, a noted instructor in Woburn, and later he attended the scientific lectures of Professor Winthrop of Harvard, in company with close friend Benjamin Thompson, afterwards the famous Count Rumford. On their return, the two students would build crude instruments illustrating the principles they had learned.

Originally a cabinet maker by trade, upon the commencement of the Revolutionary War in 1775, Loammi Baldwin enlisted in the foot regiment commanded by Colonel Samuel Gerrish. After Colonel Gerrish's retirement in 1775, Major Baldwin was elevated to head the regiment and was soon promoted to Colonel. Colonel Baldwin's regiment had been stationed in Boston, and in April of 1776, he followed General Washington to New York, and his regiment was involved in the capture of Hessian troops at Trenton. Colonel Baldwin was honorably discharged in 1777 because of ill health, and he returned to Woburn where he entered into partnership with Josiah Pierce, operating a general store and sawmill and purchasing real estate in Massachusetts and Maine for lumber and property investment. This partnership was dissolved in 1802, but Pierce continued to act on Loammi Baldwin's behalf long afterwards.

Loammi Baldwin's life was also marked by a distinguished civil career. From 1778 to 1779, he served as a representative for Woburn to the General Court, and he was again a member from 1800 to 1804. In 1780, he was appointed the first High Sherriff of Middlesex County, a post he held until 1794.

Loammi Baldwin's professional career was highlighted by his involvement as a leading proponent of the Middlesex Canal, one of the most ambitious engineering projects of its time. He served as the chief engineer of the canal, and he supervised every phase of its construction. Loammi is also remembered for discovering and developing the famous Baldwin apple which bears his name.

An honorary graduate of Harvard College (A.M. 1785), Loammi Baldwin was also a member of the American Academy of Arts and Sciences. He married Mary Fowle, daughter of James Fowle, in 1772, and in 1791, he married her cousin, Margery Fowle, daughter of Josiah Fowle. Loammi Baldwin died on October 20, 1807, following a long illness. He was survived by six children, four from his first wife (Cyrus, Benjamin, Loammi, and James) and two from his second (Clarissa and George).

Cyrus Baldwin (1773-1834), the first child of Loammi and Mary (Fowle) Baldwin, was born at Woburn on June 22, 1773. He assisted his father in building and maintaining the Middlesex Canal, and after his father's death, moved to the head of the canal at Chelmsford in order to act as its agent. He also assisted on other canal projects, most notably the Amoskeag Canal, and he was appointed inspector and sealer of gunpowder to Hale's and Whipple's factories in Lowell. He married Elizabeth Varnum of Dracut on April 28, 1799, and his only child, Mary (1802-1824), died of a "bloody fungus" on her arm and shoulder. Cyrus Baldwin died at Chelmsford on June 23, 1834.

Benjamin Franklin Baldwin (1777-1821), the second son of Loammi and Mary Baldwin, was born at Woburn, December 15, 1777. He married Mary Brewster Coolidge, daughter of Benjamin and Mary Carter (Brewster) Coolidge, on May 1, 1808. Like his brothers, he assisted his father on the construction of the Middlesex Canal, participating at different times as laborer, surveyor, and supervisor. Benjamin was a well-reputed surveyor and draftsman, and he devoted himself to several engineering projects. The most notable of these projects were his surveys for internal navigation improvements in North Carolina conducted from 1816 to 1817 and his assistance to his brother, Loammi, in the construction of the mill dam across the Back Bay in Boston.

Previous to these projects, Benjamin Baldwin was a member of the Massachusetts Militia, attaining the rank of Sergeant in 1797, Ensign in 1799, Captain in 1800, Major in 1806, and Colonel in 1811. In 1814 he resigned his commission. Also in 1814, he was appointed Justice of the Peace of Middlesex County, a post he held until his death in 1821. Throughout his life he also conducted the business of a yeoman, and it was during his return from a cattle show in Brighton that he suddenly died on October 11, 1821, at the age of 43. Three children survived him: Loammi (1813-1862), Mary Brewster (1815-1854), and Clarissa Coolidge (1819-1900).

Loammi Baldwin (1780-1838), who has been described as the "Father of Civil Engineering in America", was born May 16, 1780, the third son of Loammi and Mary Baldwin. He graduated from Harvard College with the famous class of 1800, which included Washington Allston, Charles Lowell, Lemuel Shaw, and Joshua Bates, having established a penchant for mechanics and engineering. He was discouraged from following engineering as a profession, however, because of the cost and the long term of apprenticeship, so he turned his attention to the study of law. After admission to the bar in 1804, he opened an office in Cambridge where he practiced law for three years.

In 1807, Loammi abandoned his law practice in order to study civil engineering, and he travelled to England in order to examine its public works projects. He returned to America the same year and opened an office in Charlestown. His first major project came in 1814 when he was appointed engineer to rebuild Boston's military defenses, and he designed and built Fort Strong on Noodle's Island. From 1817 to 1820, he worked on various public works projects in Virginia, and in 1819, he was appointed to construct Boston's mill dam. In 1821, Loammi Baldwin was appointed engineer of the 79-mile Union Canal in Pennsylvania, but he left this position after a conflict with the canal's president over the project's design. Later, Baldwin's design was found to be correct, and the alterations were made at a great expense.

In 1825, following a year spent in Europe, Loammi Baldwin was appointed one of the directors of the Bunker Hill Monument along with Daniel Webster, Washington Allston, and Gilbert Stuart. In the same year he began surveying a route for a canal from Boston Harbor to the Hudson River, and in 1827, he was again appointed to survey the same route, this time for a railroad line. Loammi Baldwin was forced to delegate responsibility for this latter survey to his brother James, however, because in the same year, 1827, he embarked on the most ambitious engineering project of his career, the construction of the naval dry docks in Charlestown and Norfolk. The dry docks were finished seven years later, in 1834, and Loammi began surveys on a third dry dock in New York Harbor, but this project was delayed and wasn't built until after Loammi's death. Also in 1834, Loammi Baldwin published the "Report on the Subject of Introducing Pure Water into the City of Boston", and he wound up his engineering career in 1836 with the "Report on the Brunswick Canal and Railroad, Glynn County, Georgia".

Loammi Baldwin married Ann Williams on May 5, 1816, and in 1817, his only child, Samuel, was born. Five years later, on December 28, 1822, Samuel died. In 1828, Loammi married his second wife, Catherine (Williams) Beckford, widow of Captain Thomas Beckford and sister to Samuel Williams, an American banker and financier living in London. Together they had no children, but Catherine had three children from her previous marriage, one of whom, Catherine Richardson Beckford (1813-1873), would marry Loammi's half-brother, George. In 1837, Loammi Baldwin suffered a paralyzing stroke, and nearly a year later a second attack proved fatal; Loammi died June 30, 1838, at the age of fifty-eight.

James Fowle Baldwin (1782-1862) was born in Woburn, Massachusetts, on April 29, 1782, the fourth son of Loammi and Mary Baldwin. He studied at the academies in Billerica and Westford, and he settled in Boston as a merchant. Like his father and his brothers before him, however, his attention also spread to the field of civil engineering. He retained his ties to the mercantile business, but he also became involved in a number of engineering projects. From 1827 to 1834, he assisted his brother, Loammi, on the survey and construction of the Charlestown and Norfolk dry docks; in 1828, he assisted on the survey of a railroad from Boston to Albany, and from 1830 to 1835, he was employed in the construction of the Boston and Lowell Railroad and in the planning of the factories which bordered it. From 1837 to 1848, James Baldwin also contributed to the introduction of pure water into the city of Boston, and his recommendation that Long Pond (Lake Cochituate) be used as a water source was the singular factor leading to the project's success.

Among his other achievements, James Baldwin was elected to a term as State Senator for Suffolk County in 1845, and he also served for several years as a member of the State Water Commission. He acted as friend and agent to Sarah Thompson, the Countess of Rumford, daughter of the famous Benjamin Thompson, Count Rumford, and he served as administrator of her estate. A member of the American Academy of Arts and Sciences, James also continually encouraged and assisted young students who were learning the field of civil engineering.

James Baldwin was married to Sarah Parsons, daughter of the Honorable Samuel Pitkin of East Hartford, Connecticut. Together they raised three sons, none of whom lived into adulthood. Samuel, the middle son, died in 1829 at the age of eight, and James and Cyrus died of typhus fever in 1834 at the ages of 15 and 6, respectively. James, who had enjoyed particularly good health all of his life, passed away suddenly on May 20, 1862, at the age of eighty.

George Rumford Baldwin (1798-1888) was born on January 26, 1798, in the Baldwin Mansion at North Woburn, the second child of Loammi Baldwin (1745-1807) and his second wife, Margery. He was given the name Rumford in honor of the close association between his father and Benjamin Thompson, Count Rumford. As a child, he showed a marked aptitude for mathematical and scientific studies, and he was encouraged by his older brothers to enter the field of civil engineering. He assisted his brother, Loammi, on the drawing of the plans for the fortification of Boston Harbor in 1814, and in 1822, while still a young man, he built the graceful elliptical stone bridge over the Middlesex Canal near Medford, Massachusetts.

From 1823 to 1825, George Baldwin was a consulting engineer for the redevelopment of the Pawtucket Canal and factory system at Lowell, Massachusetts, and in 1826, he was called upon to survey the Charlestown Navy Yard. He designed and built the Boston Marine Railway shortly afterwards, and his labors were such a success that in 1833 he was hired to design the Lowell Railroad. Later, in 1845, he was appointed the chief engineer for a survey of the route for the Buffalo and Mississippi Railroad.

George Baldwin's chief interest, however, lay in hydraulic engineering, and he is most well-known for his work as the designer and superintendent of the Quebec Water Works in the 1850s and as a consulting engineer for the Mystic Water Works in Charlestown in 1860. In 1861 he was appointed by the State Legislature to be the engineer of the proposed Cape Cod Canal, and in 1867 he operated as State Engineer for improvements in Boston Harbor.

In 1837, George married Catherine Richardson Beckford, the daughter of his brother's wife by a previous marriage. His domestic ties were strong, and he took his role as the last surviving brother of the Baldwin family seriously, overseeing the family's land holdings and generously assisting family members undergoing hardship. Because of the nature of his work, George Baldwin was continually traveling, and he found it necessary to maintain two residences, one at the Baldwin Mansion in North Woburn, and the other at the "Rumford House" in Quebec. He died on October 12, 1888, in the house where he was born 90 years earlier. He was survived by his only child, Catherine (Kitty) Rumford Baldwin, who lived in Quebec with her second husband, William Griffith.