Wang (王) is the most populated surname in the world, with a population of ~107 millions (see: Wikipedia, Forebears), making it the 16th most populated country. It is slightly lower than the combined population of the four most populated states (CA, TX, FL, NY), which is ~114 millions.
It is difficult to have an accurate frequency of initials in Chinese characters, especially for characters in names. Let’s just use page count in Xinhua Dictionary (12th edition) as an approximation. The total page count is 664, whereas for C the page range is 40 to 79, which is ~6%.
Therefore, for C. Wang, the estimated population is 6.42 millions, making it the 110th most populated country in the world, or the 18th most populated state in the US.