“Do most Christians believe in young earth creationism?”
No. Most young earth creationists are in the US, but US Christians make up only a small percentage of all Christians worldwide. But if you are asking specifically in the US context, the answer still seems to be no.
Exact numbers are hard to find because how one asks the question affects the results. If you ask people to pick which of three views is closest to their personal beliefs, about 40% of Americans choose something akin to young earth creationism. The obvious problem here, however, is that something akin to young earth creationism being closest to one’s beliefs is not the same thing as believing in young earth creationism.
On the other hand, if you ask people about the specific tenets of young earth creationism, about 10% of Americans will consistently commit to the view. People aren’t always consistent, however. Case in point, another survey discussed in the same article found that 18% of respondents agreed with the statement “the earth is less than 10,000 years old” while simultaneously finding that 39% agreed with the statement “God created the universe, the earth, the sun, moon, stars, plants, animals, and the first two people within the past 10,000 years” despite the fact that the first claim is contained within the second (which means that the first statement shouldn’t receive a lower rate of agreement than the second).
Nevertheless, insofar as “most” means “more than 50%,” the available data suggests that most Americans are not young earth creationists.
“True Christians believe in using one’s God given brain to learn about the world, not to restrict one’s thinking.”
“Well, christians that do not believe in young earth creationism and the literal interpretation of the bible, are not real christians.”
Two appeal to purity fallacies in the first six answers, and they go in opposite directions. Truly a sight to see.