According to a recent Gallup poll regarding ideology, "conservatives" made up the largest segment of the population. The study asked people to describe their political views. 40% of Americans call themselves "conservative" as opposed to 35% who define themselves as "moderates" and 21% who label themselves as "liberal". These results were compiled from over 40,000 interviews with American individuals since the year 2009 began.
To read more: http://www.gallup.com/poll/120857/Conservatives-Single-Largest-Ideological-Group.aspx