There are many strategies for finding relevant US government resources. As stated above, a great starting point is the UCSD US Government Information Research Guide. The databases, websites, and print guides/indexes listed below are also excellent. Several of these resources will help you identify specific publications (with call numbers that you can browse around to find more) that will have information on your topic. Finally, you can simply go to the shelves with print documents (Geisel 2W) and browse by call number. In order to find out which call number to browse in, you need to understand that US government documents and publications are organized by the Superintendent of Documents (SuDocs) Classification Scheme, which is based on US government agencies. In order to find out what letters (stems of classification numbers) have been assigned to different agencies, you can use the list (scroll down to the bottom of the page) provided by the US Federal Depository Library Program.
For the COVID 19 Crisis, we have access to GPO Masterfile (accessible from ROGER) which provides a bibliography covering all 245 years of U.S. government publications—twenty-seven collections with a single search and access to over 9.5 million links to digital content, including full-text printed material, maps, photographs, illustrations, and statistical datasets.
Please note that I have listed the following resources are in order of my own preference (mostly because of ease of searching), but all resources below are very important.
Congressional sources provide information on virtually every topic imaginable, including any topic in foreign relations or in another country with which the US government was/is concerned. Congressional Research Service (CRS) reports are often excellent starting points for research topics, because these are studies carried out by subject experts at the Library of Congress for government employees and members of congress, and included excellent summaries and bibliographies.
An independent non-governmental research institute and library located at The George Washington University, collects and publishes declassified documents obtained through the Freedom of Information Act. It provides the most comprehensive collection available of significant primary documents central to US foreign and military policy since 1945. UCSD LIbrary also subscribes to its supplementary database, the Digital National Security Archive which provides additional information.
U.S. Declassified Documents Online 
Full text of documents from various government agencies: the White House, the CIA, the FBI, the State Department and others, declassified by the U.S. government, and obtained from Presidential Libraries.
Digital National Security Archive
Provides access to nearly 40,000 declassifed government documents from 1945 to present, organized into collections, each focused on a single topic. See also the National Security Archive website, which provides access to additional documents and information.
Foreign Relations of the United States
Official diplomatic record of U.S. relations with other countries. Contains important speeches, communiques, and other communications of State Department officials and diplomats. There is a delay (approximately 30-40 years) in the release of information as it becomes declassified.
Reports from U.S. Diplomats stationed in particular Latin American Countries, Including:
Confidential U.S. State Department Central Files
Dispatches/Despatches from U.S. Consuls and Ministers in Specific Countries Between 1783 and 1906
The Confidential U.S. State Department Central Files are reports by diplomats on the political, military, social, and economic events and developments in the countries in which they are stationed. As such, they have unique and very important information for researchers. UCSD Library holds a number of these in microform, print, and online formats. These are catalogued individually in UC Library Search, but the titles vary -- so it is best to run a number of searches -- such as Confidential U.S. Department of State, Confidential State Department, Confidential U.S. State department, and Records of the Department of State. It is also necessary to use the spelling "despatches" to find many of the consulate information.
To start looking for the particular set of documents that you need, consult the U.S. National Archives and Records Administration (NARA) lists below:
U.S. National Archives and Record Administration (NARA) Department of State Central Files
Once you’ve acquired information from the lists above (the name of the country, years, possibly the decimal/filing number), these can be found in different places:
Proquest History Vault (scroll down to find the Confidential State Department Central Files)
World Scholar Latin America and The Caribbean
Gale Primary Sources: Archives Unbound
Some, but possibly not all, of the sources included in the above databases can be found in UC Library Search
Catalog of US Government Documents
Keyword Searchable Online Index to Government Documents Provided by the U.S. Government
Federal Digital System (FDsys)
GPO's Federal Digital System (FDsys) provides public access to Government information submitted by Congress and Federal agencies. It includes the content previously available in GPO Access and more.
Guide to Federal Records in the National Archives of the United States
1995 Print Version available in :
US Docs, Geisel Floor2 West AE 1.108:G 94 (3 vol.)
The index to this guide is very helpful in identifying relevant collections in microfilm and other formats which can be used at the Archives themselves, or, in many cases, at other libraries. UCSD holds some of these and many others can borrowed through inter-library loan. Such holdings include copies of many collections from foreign archives.
US Government Documents Registry
Online, Keyword-Searchable Index to Government Documents Provided by the Haithi Trust
Historical Statistics of the United States
Although this ebook draws on various sources of information, government information, government resources comprise a significant portion of these.
Excellent starting point to identifying and accessing government resources.
The UCSD (US) Census Research Guide has many more search suggestions than are listed here, but here are a few useful sites and databases to know about:
There are many resources provided by UCSD Library and others' to search for Latin American Census Information:
1. Online Family Search Library (The Church of Jesus Christ of Latter Day Saints in Salt Lake City)
The online collection holds digitized versions of much of the microfilm created by the Church and housed in its physical Library.
To search for and access material for a particular region, create an account and go to the FamilySearch Wiki:
Use the Map or “Search By Place and Topic” box. This will bring you to a country specific page where you can search for a more specific term or use the facet menu on the right to identify particular kinds of records and collections (church, census, etc.)
For an example of how to use the Family Search Library Wiki to find particular materials, see the instructions on accessing the Mexican Padrones
2. A helpful resource to identify existing information -- which may be digitized on the wiki is the following:
Call Number: Geisel Reference Floor 2 West HA755 .G85 1990
Publication Date: Boston, MA : G.K. Hall, 1990
3. The Library has purchased Datasets for relatively recent censuses in a number of Latin American Countries
All of these can be found in the “Latin America Census Collection” and accessed with AD login on the X: drive in the GIS Lab.
4. Mexican Census Material:
The Instituto Nacional de Estadistica y Geografia (Mexico) provides access to much contemporary and historical Mexican census data
To get to Mexico’s first census (the Padrones, gathered between 1752-1865) (as well as additional Census Material) in the Online Family Search Library Wiki
> search for Mexico, which will take you to the Mexico Genealogy Page.
> Clilck on “Census” under record type on the left (please note that you can also search for other formats and collections of vital statistics) OR search for Padrones
(Either brings you to the Mexico Census page)
> Scroll down and click on: Padrones, 1752-1865
Once you are in, scroll down and click on the camera to access different sections of digitized microfilm.
Scroll down – click on the camera icon
