In the late 1830s Ripley became increasingly engaged in "Associationism," an early Fourierist socialist movement. In October 1840 he announced to the Transcendental Club his plan to form an associationist community based on Fourier's utopian plans. Later in 1840 and 1841 he convinced many of the club's members (though not Emerson) to join him in the enterprise, or to visit the community. On March 28, 1841, Ripley gave a farewell sermon to his failing Purchase Street parish, and in April he formed the community at Brook Farm.
The community failed in 1847 after a fire bankrupted Brook Farm and nearly ruined Ripley. His wife had converted to Catholicism in 1846, encouraged by Orestes Brownson, and had become doubtful of his Associationist politics; their relationship became strained by the 1850s. George Ripley began to work as a freelance journalist, and in 1849 was employed by Horace Greeley at the New York Tribune and also edited Harper's Magazine. Together with Bayard Taylor he compiled a Handbook of Literature and the Fine Arts (1852). Later he found a steadier income by publishing the New American Cyclopedia (16 volumes); between 1858 and 1863, it sold in the millions and earned Ripley over $100,000. In 1861 Sophia Ripley died. George Ripley remarried, to Louisa Sclossberger, in 1865, and was a part of the Gilded Age New York literary scene until his death in 1880. The biography of George Ripley (1882) was written by Octavius Brooks Frothingham.