Synthia, as her name is sometimes spelled, was the grand-daughter of Thomas Warton/Wharton & Mary Ash of Nottingham, England. They lived in Nottingham where they were associated with the textile and lace-making industry which was the focus of the city of Nottingham. Cynthia Belfield Johnston's mother, Cynthia Belfield, was born, baptised in Nottingham. (1785-1862). Cynthia's mother was a Nottingham 'girl' who grew up and was married there. Her marriage to Henry Belfield is cited as 16 Jan 1807, Saint Mary's parish, Nottingham, Nottingham, England (see p. 258, Nottingham Parish Registers). Cynthia Belfield Johnston's father was Henry Holmes Belfield (1789-1872), a skilled artisanal inventor and manufacturer of machinery, some of which were looms for making lace stockings and other hosiery. At the beginning of the 19th century Nottingham was the center of the lacemaking industry of England. Cynthia Belfield Johnston, and 6 of her siblings were born and baptised in Nottingham. Their parents and 6 siblings migrated in 1820 to Philadelphia first living in Maryland where 2 more siblings were born.

The Belfield family emigrated to the United States in 1820s, partly to escape the severe unrest and riots of the conflicts which arose in the 1820 in Nottingham. This was caused by the abrupt displacement of the artisanal (hand-knitted) lace-makers by industrial lace-making machines and semi-skilled lace workers to manage the machinery. New faster looms for making lace had been invented, possibly by her father Henry Belfield himself and other clever people like him. Cynthia's parents determined to seek a calmer life away from the shootings and killings, as the army had been sent for to quell the rioting. Her father went to Philadelphia to secure the family a living and then sent for his family who immigrated in 1820. Her father employed his skills as a machinist/inventor to establish a new business, H.H. Belfield (later H.H.Belfield & Son). At that time, this decision as a good one, as Philadelphia was a city with a thriving industrial centre which was developing many new business, including the textile sector. Cynthia's father Henry's business made valves and other devices for heavy engineering uses. Henry Holmes Belfield and Cynthia Wharton Belfield and their children initially near Baltimore, before they eventually moved to Philadelphia. With the exception of Cynthia (Belfield Johnston) and her 5 siblings who emigrated to Philadelphia, two further Belfield children were born in Maryland.

She was the wife of James Eaton Johnston (1811-1876). He was also a skilled machinist who emigrated from Scotland in 1816 to Philadelphia, also looking for a job and a better life. They were married on 14 Aug 1844, in the Presbyterian Church, Philadelphia, Philadelphia co., Pennsylvania

Cynthia Belfield's sisters and brothers are:

- Thomas Holmes Belfield (1807- 1889) [born England] married
Anna Elizabeth Marshall (1810-1884)

- William Thomas Belfield (1809-1900) [born England] married Selener Emily Marshall (1808-1875)

- Henry Holmes Belfield (1815-1890) [born England] married Elizabeth Broom (1820-1895)

- Ann Belfield,(1812 -1904) [born England, died in Bentonsport, Iowa] She married William Appleton (1805-1865) [born in Philadelphia, Pennsylvania, died in Bentonsport, Iowa].

- Maria Louisa Belfield (1818-1900) married Isaac S. Tussey (1814-1876)

- Mary Virginia Belfield (1824-1910) married James Farren (1819-1889)

- Alfred Belfield (1822-1886)[born Maryland] married Maria Johnson (1829-1911)

Children:
-- Dr. James Eaton Johnston (1845–1927), b. in Philadelphia, Philadelphia co., Pennsylvania, d. in Santa Monica, Los Angeles, California

-- Wilfred Hall Johnston (1847–1849), b. in Philadelphia, Philadelphia co., Pennsylvania, d. in Philadelphia, Philadelphia, Pennsylvania

-- Emma E. Johnston (Abt 1844 in Philadelphia, d.?)

-- Jane 'Jennie' H. Johnston (1851–1928), b. in Philadelphia, Pennsylvania, d. in Chicago, Cook County, IL

-- Anna M. E Johnston (1854–1920), b. May 1854, b. in Philadelphia, Philadelphia, Pennsylvania, d. in Chicago, Cook, Illinois

-- Walter Lincoln Johnston (1859-1923),b. in Hamilton, Hancock, Illinois, d. Portland, Oregon

-- Abraham L. Johnston (1859- ) b. 1859 in Hamilton, Hancock, Illinois,