Countries Statistics API

You could take a look at the United Nations Demographic Statistics on Azure Marketplace. http://datamarket.azure.com/dataset/unitednations/demographi...

http://datamarket.azure.com/browse/data?category=demographic...

You could try scraping the CIA World Factbook, which should have all of that information. There's no formal API, but someone has written a scraper[0] that you could rerun to get newer data (or, for that matter, you could write your own scraper).

[0]: https://github.com/twigkit/worldfactbook-dataset

Have you tried looking at the World Data Bank?

http://databank.worldbank.org/data/home.aspx