Yeah. They were, at least.
The Illuminati came into being on May 1, 1776 as the Order of the Illuminati, or the Bavarian Illuminati, as it's known today. While not much is known about the group (most of what's written about them is in German), they began as a secret society, initially with five members—that would go on to include dukes and literary men in Bavaria—who opposed the Roman Catholic Church's power over science and philosophy, and who sought to free themselves from the church and restrictions of the government. This is the Age of Enlightenment we're talking about here, so they also wanted to "enlighten" people about their superstitions and prejudices.
But, like most secret societies, they didn't stay very "secret" for long, and people gossiped about the mission of the group. Some believed they were behind the French Revolution and had their eyes on other governments to take down.