I don't know. It may depend on the 'knowledge'. Choosing to be ignorant about actual information on disease treatment can lead to severe unhappiness, when it turns out it's too late to treat anything. In certain personal cases not knowing something might lead to less unhappiness, but not happiness as such, at least in my opinion. Would you be happier in a marriage not knowing your spouse is cheating on you? I think the answer to that is no. You'd be just as happy as you'd be if he or she wasn't cheating. Not knowing wouldn't increase your happiness, it would just decrease unhappiness - and even that is only in potentia. Since you can't possibly predict what's going to happen to you even in the near, let alone distant future, knowing something that would make you temporarily unhappy could lead to increased happiness later on. And vice versa, of course.
The same goes for a lot of knowledge out there. Not realising something is wrong may make you happy now, but when shit hits the proverbial fan it could make you far more unhappy.
Then there's a problem with happiness. Some people are actually happy when they're seemingly miserable, some are happier knowing stuff, even if it's bad, some feel happy sticking their heads in the sand. I believe happiness is far too subjective to reduce it to 'ignorance is bliss' or its opposite.