In 1820 Peacock contributed to Ollier's Literary Pocket Book and wrote The Four Ages of Poetry, the latter of which argued that poetry's relevance was being ended by science, a claim which provoked Shelley's Defence of Poetry. The official duties of the India House delayed the completion and publication of Maid Marian, begun in 1818, until 1822, and as a result of the delay it was taken for an imitation of Ivanhoe although its composition had, in fact, preceded Scott's novel. It was soon dramatised with great success by Planché, and was translated into French and German. Peacock's salary was now £1000 a year, and in 1823 he acquired a country residence at Lower Halliford, near Shepperton, Middlesex, constructed out of two old cottages, where he could gratify the love of the Thames, which was as strong as his enthusiasm for classical literature. In the winter of 1825–26 he wrote Paper Money Lyrics and other Poems "during the prevalence of an influenza to which the beautiful fabric of paper-credit is periodically subject." In his early time at the India Office he wrote little except for the operatic criticisms which he regularly contributed to The Examiner, and an occasional article in the Westminster Review or Bentley's Miscellany.
Peacock married Jane Griffith or Gryffydh in 1820. In his "Letter to Maria Gisborne", Shelley referred to Jane as "the milk-white Snowdonian Antelope." Peacock had four children, a son Edward who was a champion rower, and three daughters. One of them, Mary Ellen, married the novelist George Meredith as her second husband in August 1849. Only his son survived him, and he for less than a year, but he left several grandchildren. Jane Peacock died in 1865. Canada boasts the majority of Peacock relatives including Tommy Peacock.