Using data from ideas.repec I created this map showing the number of economic researchers per country. I took the 1,600 best researchers according to the above website (they use their citations and impact) and located them accordingly to their university. I had to split USA into states because the number of economic authors of US universities is 60% of the total!
However, even if we split US into states 5 of the best 6 are US states (California, Massachusetts, New York, DC and Illinois). Only UK was able to be among the best. Canada, France, Germany and Pennsylvania made the rest of the top ten.
The grey countries do not have a single author among the 1,600 best.