What percentage of US Christians are Dispensationalists?

Within the context of your question, I take dispensationalism to mean those Christian denominations who believe the Church has NOT replaced Israel in God’s program and that the Old Testament promises to Israel have not been transferred to the Church, that God is not finished with Israel and that Israel will feature prominently in the tribulation period before the millennial reign of Christ is established. It is my understanding that Catholics, Anglicans, Latter Day Saints and Jehovah’s Witnesses believe they have replaced Israel (spiritually speaking).

The United States has the largest Christian population in the world, with nearly 240 million Christians. Source: https://en.wikipedia.org/wiki/Christianity_in_the_United_States

From the total number of Christians in the U.S. in 2017 240 million

Subtract all the Catholics 70.4 m

Subtract all Latter Day Saints (Mormons) 6.6 m

Subtract all Jehovah’s Witnesses (neither Protestant nor Catholic) 2.5 m

Remainder of Christians in the U.S. 160.5 m

That leaves an approximate number representing non-denominational Bible churches, some Baptists, Pentecostals, and Charismatic groups who subscribe to dispensationalism. Not sure where Anglicans or Methodists stand on dispensationalism and Israel, but they come under Protestant. I suspect that the total percentage of Christians in the U.S.A. who uphold the dispensationalist view that the Church has NOT replaced Israel in God’s program and that the Old Testament promises to Israel have not been transferred to the Church is not as high as some might suspect, given the lack of statistical information about non-denominational, evangelical and charismatic groups.

Disclaimer: I am a complete dunce when it comes to maths, ending up in the bottom of my class at school. Also, I know nothing about demographics or how statistics are arrived at, but here are my sources:

Source of statistics for U.S.A. in 2015: https://en.wikipedia.org/wiki/Christianity_by_country

Catholics in the U.S. 70,412,021 (22% of population) (2017) https://en.wikipedia.org/wiki/Catholic_Church_in_the_United_States

Jehovah’s Witnesses in the U.S. 2.5 million (0.8% of population) (2017) https://www.jw.org/en/publications/books/2017-service-year-report/2017-grand-totals/

https://en.wikipedia.org/wiki/Demographics_of_Jehovah%27s_Witnesses

Latter Day Saints in the U.S. 6.6 million (9.2 m North America, 16.1 m worldwide) https://www.mormonnewsroom.org/facts-and-statistics/country/united-states

EDIT: I am not trying to come up with "an accurate number" because that would be utterly impossible given the confusion within various sources of demographic information available. Below is a Wiki link for the religious demographics of the United States. Make of it what you will, bearing in mind that there are zero statistics to say how many Protestant denominations support Israel:

https://en.wikipedia.org/wiki/Demography_of_the_United_States#Religion

I can't find any surveys that asked Americans about dispensational belief directly. Dispensational theology is mainstream in evangelical Protestant circles, though being an evangelical doesn't necessarily mean one believes in premillenial dispensationalism. Many people probably do not have fixed theological positions, and cannot fairly be said either to believe or disbelieve dispensationalist theories. There are also theologically conservative Protestant churches that might not be called "evangelical" that hold to dispensationalism. I would guess that the number of evangelicals in the US provides an upper bound on the number of dispensationalists. According to the Pew Research Center, as of 2014 about 25% of Americans are evangelical Protestants.

More directly relevant to the reasoning behind the question, a Pew Research Center study from 2003 reports that 36% of Americans (of any religion) say that Israel fulfills Biblical prophecies about the Second Coming. I don't see why you would have to believe in dispensational eschatology to believe that, though. For example, 25% of Catholics said they believed Israel fulfills Biblical prophecies, and official Catholic doctrine is not dispensationalist. Of course, ordinary Catholics may not conform to official doctrine, and I'm pretty sure the official Catholic doctrine is that the state of Israel has no religious significance.

That study also reports that 63% of self-identified evangelicals believe Israel fulfills Biblical prophecies. Again, not all of them are necessarily dispensationalists. One could also, in theory, be a dispensationalist and not think the current state of Israel is the fulfillment of prophecy, but the dominant dispensationalist view says it is. If we assume that nearly all evangelicals who think Israel fulfills prophecy are dispensationalists, and that those who think it doesn't are not, and we assume that 63% of evangelicals still think Israel fulfills Biblical prophecy in 2014, then we might take 63% of 25% = 16% of Americans as a lower bound on the number of dispensationalists. Since about 80% of Americans are Christian, that would be about 20% of Christians. But I've made some pretty suspect assumptions here. My guess is that between 15% and 25% of Americans are not not dispensationalists; that is, their beliefs are basically consistent with dispensationalism, even if they don't have articulated eschatological beliefs.

One addendum: the 80% of Americans who are Christians excludes people of no religion, who mostly come from Christian families. Only about 5% of Americans identify with a non-Christian religion.