
You may or may not be aware that this week the National Archives posted online the 3.8 million pages that made up the
1940 census. They aren't yet searchable by name, but they are browsable by "enumeration district." This means that if you don't mind waiting for huge images to load, you can in essence wander from street to street and find out
all manner of information about the people who lived there 72 years ago.
Since I've had a little bit of experience with census digging (I did a lot of my family's geneaology back in the early 2000s, before I began some other project that soon sucked up all my free time), I took a few minutes and found the links to the five enumeration districts that cover Near Southeast, along with the
map that shows their locations.

So, if you live in Capitol Quarter,
ED 204 covers you (from 2nd to 5th and Virginia to M).
ED 203 goes east from 5th to 11th, while
ED 205 includes all the blocks between 2nd and South Capitol north of M, for you Velocity/Onyx/CHT/Capitol Yards folks.
ED 206 goes from M to the Waterfront and over to what's now the WASA site, while
ED 207 covers the Navy Yard, which at that time ran from New Jersey Avenue to 11th. (It's actually funny how those boundaries from 72 years ago do a pretty good job of reflecting how the neighborhood's various sub-areas are still seen today.)
This was more than 10 years before the Cappers were built, but the neighborhood wasn't exactly a rich enclave. Plus, not many houses that were standing in 1940 remain in existence today, so only a few people will get the fun of seeing who actually lived in their house back then. But I thought one or two people might enjoy wandering through the many pages to get a feel for the people who lived in Near Southeast as World War II was looming. (You'll probably want to use the
Questions Asked page to guide you across the columns. Note that the street name is written vertically in the first column, with the house number next. And the pages don't always perfectly follow the grid, so you may need to page through much of the ED to find the spot you're looking for. Plus, the image display is really cruddy right now, so using the option to download an entire ED and then browsing with the image viewer on your own computer might be preferable.)
Please post in the comments anything interesting you find--you'll make an old lady historian very happy.
(And I guess I might have to dig up the same information for earlier censuses. Not tonight.)