The author formulates the hypothesis that the key value which guides the reflections of John Stuart Mill about society is not freedom, as is traditionally assumed in connection with the liberal conception, but knowledge. The realisation of a free society is then shown to be one of the possible ways of achieving this value. On the basis of Rawls’ and Berlin’s interpretations of Mill, the author shows that Mill’s idea of a free society rests on a certain ground of value which is constituted by Mill’s conviction about the importance of knowledge. There follows a discussion of the aspects of Mill’s conception of society in which the problematic of knowledge seems to be more or less evident. The evidence is then bolstered by attention to an analysis of Mill’s thinking undertaken by John Skorupski and David Brink. The author also indicates that emphasising the connection between the value of knowledge and liberty in society may provide us with new perspectives when we seek an answer to the question of how, in practice, we can create a free society.