It's a word that is, as you can see from this screenshot (click to embiggen), in the OED now: ‘a form of social organization in which all members are equal in social position and responsibility, usually also having property in common; a political doctrine advocating this. Chiefly with reference to the political ideas of a group of writers and intellectuals of the 1790s, including Robert Southey and Samuel Taylor Coleridge.’
So, yes: Coleridge and Southey planned for a time to establish a Pantisocratic, utopian community in Kentucky: twelve married couples, clearing an area of land and living thereupon with all labour and possessions in common. Later they pinned their hopes upon the Susquehanna River in Maryland/ Pennsylvania. Coleridge wrote to Southey [6th September 1794] with the calculation that ‘£2000 will do’, that ‘we shall buy the land a great deal cheaper when we arrive in America than we could do in England.’ He added, rather over-optimistically, ‘that twelve men may easily clear 300 acres in four or five months’, adding that he had been speaking to an agent who ‘recommends the Susquehannah for its excessive beauty and its security from hostile Indians.’ Finally, as the project recoiled from its encounter with the Reality Principle, not least in financial terms, Southey proposed moving themselves and their wives instead to Wales, a downgrading of ambition that disappointed Coleridge muchly. In the end it all came to nothing.
The OED entry at the head of this post cites Southey as the first to use the word in print, but it was Coleridge's coinage: the root of the word being the Greek ἰσοκρατία. So: as democracy is rule by the demos, or people; as oligarchy is rule by the oligos or few, and as aristocracy is rule by the aristos or best (supposedly), so isocracy is rule by equals (as an isoscles triangle is one whose two longest sides are of equal length). Coleridge adds in the παντ-, or παν-, pan-, meaning all, to show not only that all will rule but that all will rule as equals. As Michael Murphy notes:
Ian Wylie argues that Pantisocracy was modelled on ‘the early Christian communities of the first centuries’; Kelvin Everest views the scheme as ‘a means of escape from the hostility of anti-jacobin England’ (influenced by Hartley’s Unitarianism); J. A. Appleyard reads Pantisocracy in terms of the philosophical systems of Hartley, Priestley, and Godwin; Peter Kitson examines the influence of Harrington and Puritan utopias; Leonard Deen focuses on the influence of Godwin, the Bible, and Hartley; Robert Sayre notes the coexisting traditions of the French Revolution and Romantic Utopianism; Stuart Andrews identifies a utopianism that has its roots in the American Revolution; and E. Logan explores Coleridge’s use of American travel accounts.Godwin and Priestly were certainly the most immediate inspirations, at least so far as Coleridge was concerned. Writing to Southey [21st October 1794] he announced that ‘in the book of Pantisocracy I hope to have comprised all that is good in Godwin’ [Collected Letters 1:115] ... ‘all that was good’ being Coleridge's way of announcing that he was jettisoning the humanist and atheistical ‘bad’. In other letters he added to Godwinian thought Hartley’s system of association, from The Observations on Man (1749), extrapolating from principles of mental and perceptual connection of ideas, feelings and sensations to social connections of fellowship, ethics and benevolence: ‘the ardour of private Attachments makes Philanthropy a necessary habit of the Soul. I love my Friend—such as he is, all mankind are or might be! The deduction is evident. Philanthropy (and indeed every other Virtue) is a thing of Concretion—Some home-born Feeling is the centre of the Ball, that, rolling on thro’ Life collects and assimilates every congenial Affection. [Collected Letters 1:86].