The family of Patrick McGill, Sr. was very large, and the Patrick McGill Family Papers contain the names of many different members.  However, the family members most prominently featured in the collection are Patrick McGill, Sr., Patrick McGill, Jr., and Patrick McGill West. The family lived in Frederick County, Maryland in the western part of the county. The McGill’s owned enslaved people.

Patrick McGill, Sr. was born in Locust Grove, Maryland on May 14, 1765 to John Macgill and Elizabeth Duvall Macgill. He married Eleanor Hilleary West on November 28, 1789. They had eleven children: Patrick Jr. (1790-1862), Elizabeth (1792-1825), Matilda (1794-1796), Sarah (1797-1798), Charles (1799-1833), Arabella (1801-1802), Eleanor (1804-1872), Arabella West (1806-1882), John (1809-1810), Thomas John (1812-1886), and Mary (1815-1825). Eleanor H. W. McGill died on May 17, 1837. In 1841, Patrick Sr. joined a group of local men in forming the Library Association of Jefferson, which collected "literary and scientific books" for its members to share. He died in Locust Grove, Maryland on March 30, 1848.

Patrick McGill, Jr. was born in Jefferson, Maryland on October 4, 1790. He married Mary Davis Hook on March 17, 1816 -- only to discover 3 years later that the rector who had married them did not have Holy Orders. They confirmed their marriage on April 13, 1819. That day Mary's brother James Hook also wed Patrick's sister Elizabeth McGill. Patrick and Mary had nine children: Edward West (1817-1891), Sarah (1818-1903), America (1820-1883), Patrick Oliver (1822-1852), William (1824-1852), Elizabeth (1826), Eleanora Arabella (1827-1900), Ann Matilda (1830-1892), and Mary Davis (1832-1882). Patrick purchased Mary's uncle's plantation, Potomac Hills, in 1820 and settled into the life of a well-to-do farmer. Like his father, Patrick McGill, Jr. was active in the community: he served as a Justice of the Peace in 1847. Mary Davis Hook McGill died on July 19, 1833. Patrick Jr. lived for nearly another three decades. He died in Frederick, Maryland on May 29, 1862.

Patrick McGill West was born in Frederick, Maryland on February 3, 1825 to Levin West and Eliza Hilleary West. He married his second cousin Eleanora Arabella McGill, daughter of his namesake, on May 31, 1859. West was active in the Episcopal Church, serving as a churchwarden in St. Mark's and St. Paul's Parishes. Along with Edward West McGill, he was an executor of Patrick McGill, Jr.'s will, which may be how his personal papers found their way into the collection. Eleanora died on January 25, 1900, and Patrick died on August 18, 1904.