A study made by Pitzer concludes that Sweden, Vietnam, Denmark, Norway and Japan are the least religious countries in the world. The United States is one of the countries at the end of the list.
It’s interesting that the US is the country with less percentage of atheists and Vietnam is the one with more percentage of atheists. The second country with the highest atheism level (purple bars) is Japan.
In Japan there are many religions, but the main ones are Shintoism and Buddhism. But I know very few Japanese who declare themselves “Buddhist” or “Shintoist”. Most of the people just “believes” and mixes religions, they would marry shinto style and do a funeral following the buddhist tradition. It’s all mixed, and more than believing in a religion, I would say that people is superstitious. Furthermore, Buddhism doesn’t have the concept of Creator God and Shinto is a polytheistic religions. For Japanese people is difficult to think about a God in the western sense.
This chart below shows countries based on their acceptance of the Theory of evolution. It’s interesting that there are some coincidences with the religion chart, but some countries just change the position a lot, for example Spain goes to the top 10 in this chart but the US stays at the bottom.