Jessica Ellen Hayllar (16 September 1858 – 7 November 1940) was a British artist and painter. Hayllar was born in London and was the eldest daughter of the nine children born to Ellen Phoebe Cavell (1827-1899) and her husband James Hayllar (1829-1920). The family lived at Mecklenburgh Square in London and also rented a country house in Suffolk for several months each year before moving to a large house, Castle Priory, by the Thames at Wallingford, then in Berkshire.

Hayllar and her four sisters attended a day school in Gower Street and all were given art lessons by their father, who was himself a well-regarded painter. Jessica Hayllar became the most prolific artist among the Hayllar offspring, although he...