John Grant Chapman was born in 1798 in Chapmantown (now La Plata), Charles County, Maryland. He studied law at Yale University, graduating in 1817. Chapman joined the Maryland bar in 1819 and began practicing law in Port Tobacco, also in Charles County, Maryland, shortly thereafter, in addition to running his plantation. According to U.S. Census records, the family enslaved 32 people on the plantation as of the 1800 census, nearly 70 people by 1830, nearly 90 people in 1840, and 140 people in 1850.
John Grant Chapman married a Virginia cousin, Susan Pearson A. Chapman. John Grant and Susan had five living sons: John Grant, Jr. (b. 1833?), Marshall (b. 1835?), George P. (b. 1837?), Andrew Grant (b. 1839), and Robert F. (b. 1840?). By 1840, Elizabeth Chapman, perhaps John Grant's mother, was living with the family.
An affluent citizen of Charles County, John Grant Chapman participated in both state and national politics for over twenty-five years. A member of the Whig party, he served in the Maryland House of Delegates from 1824 to 1828 and again in 1830 and was Speaker of the House from 1826 to 1828. Chapman then advanced to the Maryland Senate, serving from 1831 to 1836 and holding the positions of President Pro Tem in 1831 and President from 1834 to 1836. He returned to the Maryland House of Delegates again in 1843 and 1844 as Speaker of the House. Chapman ran unsuccessfully for governor in 1844 but was subsequently elected to the U. S. House of Representatives, serving from 1845 to 1849. In 1850, John Grant was elected president of Maryland's Constitutional Convention.
The Chapman sons left their parents' Port Tobacco estate upon maturity. Before 1860, John Grant, Jr. married Mary (whose maiden name is unknown) and began his own life as a planter. Nothing further is known about this couple or about one of the other Chapman sons, George. Robert F. Chapman attended the University of Maryland Medical School in Baltimore from 1864 to 1865. How he used his medical skills immediately after graduation is unknown, but, during the late 1860s, Robert busied himself with agricultural pursuits, joining his brother Marshall on the family plantation. In the mid- to late-1870s Robert moved to New York City to work for Bellevue Hospital.
Marshall Chapman, the second of John Grant Chapman's sons, inherited the Chapman estate upon his father's death in 1856. Sometime during the early 1860s, he married, and he and his wife, Ellen, had four daughters, Ellen S. (b. 1854?), Mary (b. 1856?), Etheldra (B. 1869?), and Nannie Kent (b. early 1870s?). Much of the personal correspondence in this collection concerns this branch of the Chapman family. The financial papers detail Marshall's agricultural work as a producer of tobacco and wheat.
Andrew Grant Chapman was the only son to follow directly in his father's footsteps and pursue law, politics, and farming. Andrew served in the Maryland House of Delegates from 1868 to 1872, in 1880, and again in 1886, when he was also Speaker Pro Tem. Andrew Grant Chapman served in the U. S. House of Representatives from 1881 to 1883 and was a delegate to the Democratic National Convention in 1888. Andrew lived with Marshall's family until he married Helen Mary Chapman in 1871, after which he farmed his own plantation. Andrew and Helen Mary had seven children.