Eugenie C. Scott gives a very nice (and thorough) overview of the development of creationism after the Scopes trial in her book Evolution vs Creationism: an Introduction. She doesn't give numbers, but she does say this:

After the Scopes trial, antievolutionism became associated in the popular imagination with conservative religious views - and with the most negative stereotypes of such views. Antievolutionists and fundamentalists in general were portrayed as foolish, unthinking, religious zealots. (...) Although may of leaders of the pre-Scopes antievolution movement were from the Northern states, after the Scopes trial, antievolutionism became more regionalized, retaining momentum in the South and rural areas of the country, where fundamentalism remained strong. (p. 102)

She goes on to mention that the teaching of evolution did decline, mostly because of economic pressures. The large textbook market in the South preferred books which slighted evolution; publishers knew that and largely removed it from the textbooks. Since textbooks have a great influence on the school curricula, evolution disappeared from classrooms, even in areas where antievolutionism wasn't very established.

Note that Scott speaks of 'antievolutionism' up til this moment, as it was not yet the same as modern day Young Earth Creationism. People considered evolution to be contradictory to their religious views and thus they didn't want it in their classrooms. It is essentially a negative option - anti evolution. Young Earth Creationism on the other hand also disagrees with evolution, but tries to put something in its stead. In that sense (and only in that sense) it is a positive option. For something instead of (just) against something.

Young Earth Creationism really got off the ground in the 1960s. After the Russian launch of Sputnik, the United States tried to shore up their science education so that they would be better able to compete with the Soviets scientifically. This led to new and improved textbooks, which included evolution as a major component of biological sciences. Furthermore, in 1968 the U.S. Supreme Court ruled that the few remaining antievolution laws (in 4 states) were unconstitutional. Both these factors, working against antievolutionism, led to pushback in the antievolutionist movement and the creation of Young Earth Creationism as we know it today.

Scott again:

[T]he modern creation science movement crystallized in 1961 with the publication of [Henry] Morris's book The Genesis Flood, written with the theologian John Whitcomb. (...) Morris provided the scientific references and Whitcomb provided the theological arguments. The book's mix of theology and science is characteristic of creation science, and it continues to be widely read in evangelical and fundamentalist circles. The Genesis Flood proposed that there is scientific evidence that Earth is less than ten thousand years old, and the evolution was therefore impossible. This view became known as young-Earth creationism. (p. 105-106)

In 1963 Morris and others founded the Creation Research Society and in 1972 he was co-founder of the Institute for Creation Research. These groups worked to spread Young Earth Creationism. In 1987 Ken Ham came to work for the Institute for Creation Research; he later went on to found Answers in Genesis, now the largest Young Earth Creationist organization.

After a few court battles in the 1980's 'creation science' was banned from the classrooms as unconstitutional, as it was essentially religion. This led to a rebranding of creation science as 'intelligent design' and more court battles in recent history. All in all, this history of antievolutionism has led to the situation today, where the United States has the lowest acceptance rate of evolution of all Western countries.

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Source:

E.C. Scott, Evolution vs. Creationism: an Introduction, Berkeley 2009

(Edit: typos)