William C. Avery was born May 31, 1819 in the Caldwell region of Essex County, New Jersey, son of Hezekiah Avery (1774-1835) and Martha Corby Avery (1777-1853). His family (including members of the Corby family) migrated to Troy Township (and surrounding area), Bradford County, Pennsylvania, probably in early 1826, based on Presbyterian Church admission records. By 1840, William had married Beulah Harvey (1818-1904), one of about a dozen born to Armenia pioneer Newton Harvey (1784-1868) and Anna Scisson Harvey (1785-1765) who migrated to the region in the 18-teens. William and Beulah had four sons and three daughters.

William's father, Hezekiah, was a veteran of the War of 1812, according to a Pennsylvania Veteran's Burial card, though service records at the National Archives have yet to be found. Following Hezekiah's death, widow Martha married John W. Freelove of New Hampshire (1772-?) on June 17, 1843. By 1850, Martha Freelove was widowed, residing with daughter Elizabeth "Betsey" and son-in-law Aruna Hart. The Harts, together with Betsey's brother Abijah Avery (and probably members of his family), left the Troy area in the early 1850s (perhaps soon after Martha's death in 1853), removing to Wisconsin. Abijah's wife, Eleanor Clifton, apparently did not accompany him, since she appears in Troy on her parents' 1860 census as Eleanor Clifton. Moreover, daughter Martha May, born 1848, lived out her life in Tioga County, Pennsylvania.

Based on church records, burial locations, DNA matches, and census records (particularly those affirming New Jersey births), the following are all presumed siblings of William:

Roxana Avery (1798-1870) m. Hiram Godard (1805-1870)
Hannah Avery (1800-1874) m. 1) Hubbard Williams (1802-1847) and 2) Joseph Harding
Sarah Avery (c. 1801-1857) m. 1) Henry N Winne (1796-1844) and 2) Nathaniel Clark (1790-)
Elizabeth "Betsey" Avery (c. 1804-1881) m. Aruna Hart (1792-)
Rhoda Avery (1807-1853) m. Peter Garabrant (1796-1852)
Abijah "Bijah" Avery (c. 1810-post 1855) m. Eleanor Clifton (c. 1813-)
Harriet Avery (c. 1813-1894) m. Ambrose Murry (c. 1812-1872)
Eleanor Avery (1818-1858) m. 1) Kennedy? and 2) Hiram Baker (1817-1894)

Note that among William and Beulah's offspring, listed below, daughters Rosalia, Hannah, and Sarah correspond, in order, to sisters Roxana, Hannah, and Sarah, above.

George Avery (1842-1899) m. Eunice R Whipple (1844-1924)

Rosalia F "Rosalie" Avery (1844-1918) m. Philetus S Whipple (1843-1921) (brother to George's wife, Eunice Whipple)

Hannah Avery (1848-1926)- unmarried - classified by the gov't. as "deaf and dumb"

Sarah O Avery (1850-1902) m. Royal Joshua Sargeant (1848-1931)

Milton Eugene Avery (1853-1872)- died at 19

Edward Franklin Avery (1855-1934) m. Elsie Ann Hill Lamb (1848-1909)

William Morell Avery (1858-1934) m. 1) Lydia M Tinkham (1860-1904) and 2) Alta May Pelletta Pye (1874-1957)

The William Avery family was listed on the 1850 census in Granville, Bradford County and in 1860 was recorded in Troy. In the 1860s, the Averys moved to McIntyre Township in Lycoming County (post office: Liberty, Tioga County, per the 1870 census).

William died April 22, 1877. About two-and-a-half months later, son Edward Franklin wrote in a letter dated July 12, 1877: "I have been making out the inventory of Father’s property. I had the appraisers here yesterday. At the rate they valued the land, Ma will hold about half the farm and the rest will not pay the debts. But that is all we will have to pay."

William C was originally interred in Ellenton's Whipple Cemetery, but was removed to Lot 85 in the present-day Ellenton Cemetery soon after wife Beulah's interment there in October 1904.