Remeber the CRAAP guidelines.
Published by the State Department, Background Notes include facts about the land, people, history, government, political conditions, economy, and foreign relations of independent states, some dependencies, and areas of special sovereignty.
Published by the Library of Congress, the Country Studies Series presents a description and analysis of the historical setting and the social, economic, political, and national security systems and institutions of countries throughout the world. We have some of these in print in the government documents collection on the 1st floor of the library, but many additional volumes are available electronically.
For example, to search for country studies in Wyndham Robertson Library, search: "country study" AND Mexico (or other country of interest).
Note the date of publication in the country study. The specific information on the current heads of state may be outdated, but the historical, contextual information can still be relevant.