The Census Bureau's data.census.gov offers free access to some data, but it's important to know that the data available there includes nothing for years prior to 2000. Many people (including me!) also find the interface difficult to use.
Social Explorer is a subscription database that the library pays for. It offers access to more comprehensive Census data, including data back to 1790. This database is also (in my opinion) much easier to use than data.census.gov, so I recommend that you start with Social Explorer to find Census/demographic data.
Social Explorer can help you identify Census tracts back to 1950.
Important information about the Social Explorer database:
To access the database from off-campus, you will need to have your computer configured to use the UCSD VPN. If you need help with that, please refer to the remote access instructions. Note that you MUST select 2-Step Secured - Allthruucsd from the "Group" drop-down menu when authenticating. If you're correctly connected via the VPN, you should see the UC San Diego notation below in the banner on Social Explorer's home page.
To identify tracts:
1. Click on “Explore” under the United States map.
2. Drill down to the area of interest. You can use the top "search address" box, double click on an area, or use the zoom + to drill down to your area. (Click and drag map to re-center.) As you zoom in, you’ll eventually see details like street names. As you mouse over an area, you'll see popups that identify the Census tract and block group numbers. Use Google maps or print maps as necessary to help identify streets, if necessary.
3. Make note of the tract numbers that comprise your neighborhood.
To get data:
There are two ways to get Census data after you've identified the census tracts.
First option: while you're still on the map showing the tracts of interest >
Second option, which I find much easier: quit the mapping application and return to the home page >
Reminder: the decennial questionnaires at Through the Decades and ACS questionnaires can be extremely helpful in figuring out what questions were asked for each census and therefore what data might be available.
Reminder: ACS tract-level data is available only for 5-year ACS, not 1- or 3- year.
Tract numbers are usually represented as a simple decimal number, such as tract 4 or tract 9.01.
Some data files, such as the Market Profile Data in SE, use an 11-digit tract number instead, such as 06073000301. This form combines the 2 digit state, 3 digit county, and 6 digit (with no decimal point) tract codes.
In the example 06073000301: 06 = CA | 073 = San Diego County | 000301 = tract number 3.01
After selecting your census tract number(s) in SE and moving to the tables page, you'll see "select a dataset" at the top of the page. The options available there depend on the year and collection you're searching.
Social Explorer tables - usually a smaller number of "popular" datasets and may compress multiple variables (e.g. individual grade levels for education attainment) into one variable (e.g. "less than high school diploma")
Summary File 1 datasets = the Census short form (i.e. everyone, or 100% data)
Summary File 3 datasets = the Census long form (i.e. sample, later ACS, data)