There is a rather eerie similarity in approach between the profoundly anti-Enlightenment Rousseau's arguments and those of latterday Islamic fundamentalists, in that both regard the emphasis on secularism and rationalism typical of the Enlightenment to be a scam and a play for power on the part of the secular and the rational. I'm sure both would be horrified at this comparison.
Although there was a significant transformation in European thought between about 1685 and 1715 (e.g. between the revocation of the Edict of Nantes and the death of Louis XIV), brilliantly summed up by Georges Hazard in his The Crises of the European Mind [orig. Fr. La Crises de la Consciesnce Europeane] with the comment "it's as if the average educated Frenchman went to bed thinking like Bishop Boussouet and woke up thinking like Voltaire", the Enlightenment proper was an 18th century, primarily a mid-18th century, phenomenon. The term 'enlightenment' itself was coined not by the French philosophes with whom most people associate the Enlightenment, but with the german philosopher Kant who used the german term Aufklaerung to describe what he and the others seemed to be about. The book to read is German philsopher Ernst Cassierer's The Philosophy of the Enlightenment. First published in German in 1935, it was translated into English in the early 50's and remains the best thing on the period. Far better than Lester Crocker (who is mostly interested in the French) or Peter Gay (who is a leftie who made his reputation by knocking Carl Becker) or any of the minor stuff.