This is an excellent guide for getting an overview of the census. Because the Census Bureau, a U.S. government agency, is moving to a new website, some links on the guide are broken, but if you contact the guide's author, Marie Concannon via the link in the guide, she can help you find the documents.
The two main ways to show data in Social Explorer are Reports (tables) and Maps. You can also create reports based on maps, which is probably the easiest way to focus on a particular tract, set of tracts, city, or county of interest to you.
The American Community Survey (ACS) is a survey of the United States based on statistical sampling, not a survey of every single U.S. household.
In Social Explorer you can use ACS data to create side-by-side maps or slider maps to compare data for geographic entities (counties, cities, census tracts, even block groups) over time, but only within the 21st century.
Social Explorer provides current and historical U.S. social data indicators from public and proprietary sources across demography, economy, health, politics, education, religion, crime, and more, at multiple geographic levels. All data are curated, documented, organized, and processed for ease of use.
Every ten years, the U.S. Census Bureau attempts to survey every single household in the United States. This immense undertaking is known as the Decennial Census of Population. The Census Bureau conducts other large surveys as well (e.g., Census of Agriculture), but when people talk about "The Census," they are usually referring to the Decennial Census of Population. It takes a long time for the Census Bureau to fully compile and publish the results, and for tools like Social Explorer to incorporate the data, so some census data from 2020 is only just starting to become available in 2024.
In Social Explorer, you can make comparisons back to 1970, using the U.S. Decennial Censuses on 2010 Geographies dataset, when creating a new Map. Once you have that dataset selected, you can set your geographic level to Tract, for urban and some suburban areas, or a larger geographic unit for rural areas, and then mask the data to select the geographic area(s) you want to look at.
If you want to compare data going back further than 1970, you will probably need to stick with County as a geographic unit. You will use the Change Data function to select the type of information you're looking for, and a particular Census to get it from, to create map comparisons.
