As a work of political philosophy without a conventional narrative, "On Liberty" does not have an actual physical setting to the arguments that take place within—but it is absolutely a product of its historical setting, in the midst of the industrial revolution and in the aftermath of the Enlightenment. Mill's ideas reflect the newfound exaltation of the individual present in much of the philosophy from the 18th and 19th centuries.
More specifically, Mill's study of the relationship between a state and the unalienable rights of the individual bears the unmistakeable mark of the 18th-century French and American Revolutions, in which the same questions were asked of government. Some of Mill's language also reflects the Industrial Revolution that had exploded across Western Europe and North America through the 18th and 19th centuries—particularly his use of metaphorical language to compare the functioning of a state to the functioning of a machine.
Finally, "On Liberty" is also a product of Mill's utilitarian philosophy. In Mill's arguments for maximizing individual liberties under the limited authority of a state or ruler, he is also arguing that the priority of a state should be to maximize the its citizens' well-being. According to this framework, the best way to support an individual's well-being is to support their individual liberties, given that such liberties that are inextricable from human dignity.