In 1922 Gerassi met Stephania Avdykovych, a Ukrainian, in Berlin and they were married in 1929. In 1931, their son Juanito (who became known as John and Tito after the family moved to the United States) was born in Paris.
Gerassi and his family moved to the United States at the start of World War II and he was hired by Carmelita Hinton, a progressive educator who was the founder and director of the Putney School in Vermont, to teach art at the school. Hinton also employed Gerassi's wife, Stepha, to teach "anything she wanted" and she would go on to teach a number of subjects during their years at the school, including French, Spanish, Russian, German, ancient history, Latin, and European history. In 1955 Time reported that to support his family while establishing his art career, he tried "some 40 different jobs". From 1944-1964 Gerassi was harassed by the CIA who tried to blackmail him by threatening to deport his family if he would not agree to work for them. One of his friends eventually reported the harassment to Abe Fortas, then an aid to Lyndon Johnson. Fortas obtained the CIA file and passed it onto the attorney general, Robert Kennedy, who immediately gave Gerassi and his family American citizenship and apologized "in the name of America".
In 1951 Gerassi shared an exhibit with American artist, Georgia O'Keeffe, and then in 1955 he exhibited alone, for the first time in 20 years. His solo exhibition at the Panoras Gallery in Manhattan "elicited rave reviews".
Gerassi returned to Putney School where he painted until his death in 1974.
Gerassi's son, John "Tito" Gerassi completed a Master of Arts at Columbia University and a doctorate at the London School of Economics. He became a journalist and worked as an editor for Time and Newsweek and then as a foreign correspondent for The New York Times. After completing his doctorate, he became an academic, teaching at John Kennedy Freedom School in Berlin and the University of California, Irvine. In 1978 joined the faculty of Queens College. His publications include, The Great Fear in Latin America(1965), The Boys of Boise (1966), and Jean-Paul Sartre: Hated Conscience of His Century (1989). Tito died in July 2012, at the age of 81.
- "Fernando Gerassi - His Art and Life". fernandogerassi.com. Retrieved 7 March 2010.
- "Art: Success through failure". Mar 28, 1955.
- Craig Savino and Jessica Weglein (July 2005). "Guide to the John Gerassi Papers ALBA 018". Tamiment Library / Wagner Archives Collection. Elmer Holmes Bobst Library. Retrieved 7 March 2010.