Seth MacFarlane (Family Guy creator) said in a interview for The Advocate that Stewie Griffin is gay. here is some of the interview
Which character do gay fans respond to the most?
Generally they respond to Stewie, because he’s arguably the most complex character. He originally began as this diabolical villain, but then we delved into the idea of his confused sexuality. We all feel that Stewie is almost certainly gay, and he’s in the process of figuring it out for himself. We haven’t ever really locked into it because we get a lot of good jokes from both sides, but we treat him oftentimes as if we were writing a gay character.
Is it odd how much people care about this cartoon baby’s sexuality?
Yeah. We’ve had letters from homophobic fans in the past, and I sort of relish the idea of saying, “Yeah, well, you know what? Your favorite character, Stewie, is gay.”