Frances Jane Crosby was born on 24 March 1820 in Brewster, New York. At six weeks a country doctor, treating a mild eye infection, applied a hot mustard poultice that permanently scarred her corneas; she was blind for the rest of her life.
Educated at the New York Institution for the Blind from age fifteen, she taught there for 23 years, married the blind musician Alexander van Alstyne in 1858, and lost her only daughter in infancy. She began writing hymn texts in her forties at the invitation of the composer William Bradbury.
"Under her own name and over 200 pseudonyms — publishers were nervous of any single writer appearing to dominate a hymnal — she produced an estimated 8,000 to 9,000 hymn texts before her death, more than any other writer in the English language. The peak years were 1868–1915, when she was under contract to the Biglow & Main publishing house for three hymns a week."
'Blessed Assurance' (1873) was composed the other way round from most hymns: the composer Phoebe Palmer Knapp played a new melody on her parlour organ, asked Crosby "What does the tune say?" and Crosby — after a moment's silence — recited the three stanzas beginning "Blessed assurance, Jesus is mine!" from memory. Knapp wrote them down.
Crosby preached at YMCA rescue missions in the Bowery slums well into her eighties and refused all offers of a share of the vast royalties earned by her texts, insisting on a $2 per hymn flat fee so that she could give the money away as she chose. She died on 12 February 1915, aged 94, at Bridgeport, Connecticut. Her tombstone was replaced in 1955 with a marker inscribed only: "Aunt Fanny — Blessed assurance, Jesus is mine."