In 2014, 43 Percent Of Americans Politically Identify As Independents: 30 Percent As Democrats: 26 Percent As Republicans: Gallup Surveys

From Gallup, "In US, New Record 43% Are Political Independents" by Jeffrey M Jones:

An average 43% of Americans identified politically as independents in 2014, establishing a new high in Gallup telephone poll trends back to 1988. In terms of national identification with the two major parties, Democrats continued to hold a modest edge over Republicans, 30% to 26%.

Source: Gallup

Since 2008, the percentage of political independents -- those who identify as such before their leanings to the two major parties are taken into account -- has steadily climbed from 35% to the current 43%, exceeding 40% each of the last four years. Prior to 2011, the high in independent identification was 39% in 1995 and 1999.

The recent rise in political independence has come at the expense of both parties, but more among Democrats than among Republicans. Over the last six years, Democratic identification has fallen from 36% -- the highest in the last 25 years -- to 30%. Meanwhile, Republican identification is down from 28% in 2008 to 26% last year.