The chart above shows the percentages of Americans believing in creationism and evolution from 1982 to the present. The information is from Gallup Polls -- the latest of which was done between May 8th and 11th of a random national sample of 1,028 adults (with a four point margin of error). Frankly, I find the chart a bit depressing, because it shows the percentage of Americans believing in creationism (the belief that god created humans in their present form within the last 10,000 years) has remained very constant for the last three decades. That was the belief of 44% in 1982 and 42% today -- an insignificant difference within the margin of error.
There are a couple of bright spots in the chart. Currently 50% of the population says they believe in the science of evolution (with 31% saying that evolution was guided by god, and 19% saying it was not). Those believing in evolution w/o god has increased by 10 points in the last three decades (from 9% in 1982 to 19% in 2014) -- but most of that growth has come from a reduction in the percentage of god-guided evolution believers rather than creationists.
The charts below show the belief in creationism/evolution by age and education. The only age group with a majority believing in evolution is the 18-29 age group, where 65% say they believe in evolution. The only educational group where a majority believes in evolution are those with a college education, where 68% say they believe in evolution.
This does help explain why it is so hard to convince Americans that something must be done about global climate change (commonly called global warming). With 42% of Americans already tossing science out the window in favor of their religious myths, it makes sense that this group would also be willing to disregard science for other reasons -- like accepting the right-wing lies that global warming is a myth, or that doing something about it will hurt the economy (neither of which is true).
