The majority of the letters in this family correspondence were directed to James Witter Nicholson (1773-1851), of New Geneva, Fayette County, Pennsylvania. Most were written by Nicholson's sisters, especially Maria Nicholson Montgomery (1775-1868), of New York and Baltimore. The Nicholsons' father, James Nicholson (1737-1804), was a Maryland native who, like others in the family then and later, went to sea at an early age. In 1763 he made an advantageous marriage to Frances Witter (1744-1832), the only child of a prosperous Bermudian merchant, and settled in New York. With the coming of the Revolution Nicholson joined the Continental navy, commanding vessels in several actions and becoming, through a Congressional resolution of October 1776, the young service's senior captain—hence the "Commodore" familiarly attached to his name in later life. After the war Nicholson turned his attention to politics. From his home on William Street, and from his summer residence at Greenwich, north of New York City, he became an influential figure in the local anti-Federalist circles, serving for a time as president of the Democratic Society of the City of New York. Four of his five daughters married men active in public life. The eldest, Catharine (1764-1850), wed Colonel William Few (1748-1828), who represented Georgia at the Constitutional Convention and served as one of that state's original U. S. Senators. Hannah Nicholson (1766-1849) was the second wife (m. 1793) of Albert Gallatin, the chief architect of Democratic-Republican financial policy and Secretary of the Treasury under Jefferson and Madison. Gallatin's intimacy with his in-laws—he typically spent a good part of the summer with the Nicholsons, at least until his departure for Europe in 1813—confirmed the family's position among New York's Republican elite, even after the death of James Nicholson in 1804. Also contributing to the family's political prominence was "Cousin Joseph," Joseph Hopper Nicholson of Maryland (1770-1817), elected as a Republican to the Sixth, Seventh, Eighth, and Ninth Congresses. The Nicholsons' third daughter, Frances (1771-1851), married Joshua Seney (1756-1798), who served Maryland in both the Continental and United States Congresses. Jehoiadden Nicholson, called Adden (1783-1828), youngest of the five daughters, married a Presbyterian clergyman named James W. Chrystie (1786-1863).

The fourth Nicholson daughter (and primary author of the letters), Maria Nicholson, did not marry until her thirty-fourth year, and so spent her young adulthood at the William Street and Greenwich homes during the heyday of the family's political influence. In 1809 she wed a Republican congressman, John Montgomery (1764-1828) of Harford County, Maryland, then in the midst of three consecutive terms in the U. S. House of Representatives. The couple moved to Baltimore in 1811, when Montgomery became state attorney general, and were still residing there during the British campaign of 1814; both Montgomery and Joseph Nicholson fought in defense of the city. Maria Montgomery would remain in Baltimore through her husband's tenure as the city's mayor (1820-26), moving back to New York only after his death in 1828. The couple's only child, James Nicholson Montgomery, died in 1814. In her later years Maria appears to have remained financially independent, though the tone of her letters darkens, and their content is increasingly informed by her Presbyterian faith. She died in 1868, aged 93.

James Witter Nicholson, the recipient of most of the letters, was the only son of James and Frances Nicholson to survive to adulthood. His settlement on the western Pennsylvania frontier was an immediate consequence of his sister's marriage to Albert Gallatin. Nicholson was one of five original investors in Albert Gallatin & Co., a partnership aimed at developing business interests along the Monongahela River in Fayette County, where Gallatin owned land. In 1795 Nicholson went west with his partners to found the community of New Geneva, working to establish a general mercantile store, mills, and subsequently a glassworks. The partnership ended in 1799, with Gallatin assuming complete ownership of the group's assets. Because Gallatin's political obligations limited the amount of time he could spend in the West, James Nicholson stayed on to oversee his interests. He would remain in New Geneva for the rest of his life, though to no enduring financial advantage; the Gallatin glassworks failed in 1822, and the rest of the western properties were sold off in the early 1830s. During the 1820s Nicholson served as New Geneva's postmaster. To judge by his sisters' letters, his later years were unhappy ones, plagued by debt, family difficulties and tragedies (including the deaths, between 1832 and 1847, of his wife and four of his children), and poor health. He died at New Geneva in 1851.