Well, one thing that is sometimes overlooked is the importance of having a governor in the settlement. Try putting a family member or general in there - preferably someone with as much Influence as possible (the governor's influence has a direct effect on public order) although Management is important as well. There are also numerous traits and ancilliares that will have a positive or negative effect on public order.

Also, if you're unsure about Public Order or Population or any other figure on the City screen, remember to check out the Details screen (the scroll button on the bottom left of the City screen) This shows a detailed breakdown of things like Public Order which should show you exactly what's driving the citizens to insurrection and revolt.

Antagonist