It’s held relatively steady:
The percentage of the U.S. population choosing the creationist perspective as closest to their own view has fluctuated in a narrow range between 40% and 47% since the question’s inception. There is little indication of a sustained downward trend in the proportion of the U.S. population who hold a creationist view of human origins. At the same time, the percentage of Americans who adhere to a strict secularist viewpoint — that humans evolved over time, with God having no part in this process — has doubled since 1999.
Hemant Mehta digs into the survey details:
[N]early a third of Millennials (ages 18-29) accepted evolution without God’s “guiding hand” compared to only 11% of Americans 50-64. The younger generation, of course, is already far less religious to begin with, so the correlation is strong. There’s hope for the future! But damn, what a grim present.
Relatedly, Dan Kahan recently proclaimed that creationist beliefs don’t indicate scientific illiteracy:
First, there is zero correlation between saying one “believes” in evolution & understanding the rudiments of modern evolutionary science. Those who say they do “believe” are no more likely to be able to be able to give a high-school-exam passing account of natural selection, genetic variance, and random mutation — the basic elements of the modern synthesis — than than those who say they “don’t” believe. In fact, neither is very likely to be able to, which means that those who “believe” in evolution are professing their assent to something they don’t understand.
Ronald Bailey adds:
Evidently many religious Americans can understand the scientists’ explanation for how evolutionary biology works while still believing in the special divine creation of Adam and Eve.