An extremely rich source of population health data from the Institute for Health Metrics and Evaluation (IHME). Besides keyword searching you can also fnd profiles of individual countries and, for some countries (United States, Brazil, Indonesia, Japan, U.K., Mexico) profiles at the state (or equivalent) level. Also explore the GBD Compare visualization tool to start manipulating some of the data. Look for the Take Tour in the first major colum to explain how to use it. GBD stands for "Global Burden of Disease". Here is a quick overview from IHME's FAQs page.
If you are doing anything related to the health of populations at the state, country (U.S. or other countries) or international level be sure to take a look at this source
The World Health Organization is an excellent place to start when looking for international or country specific health information. Look at the main site for information on a wide variety of health topics, data and country specific information. Go to the regional office websites for information focused on regions of the world plus more (often different) country information.