Some readers have asked where I get the numbers that go into posts like this. The answer is the Millennial Edition of Historical Statistics of the United States. It’s a spectacular source. The bad news is that it’s paywalled. But if you’re at a university, or have access some other way — I guess there’s a print edition too, which libraries might have — it’s great.
By the way, for more contemporary stuff I rely heavily on Eurostat and the IMF WEO database, both free, and the OECD, some free, some not.