Where can I find the record for the heaviest single-day rainfall ever recorded on any date at a specific location?
Sounds like your question, like most questions about historical data, might be a little challenging to find the right source, as it often is around the world.

But seeing you said Atlanta brightened my eyes!

For if one is seeking information for a US climate observation sites (most big cities, and a fairly reasonable web across the US... there's about 2-6 per Weather Service office), then there's a great source for historical data that, with a little looking around, allows you to fairly quickly answer quite a lot of interesting questions about your area once you get used to doing it... the NowData portal on your local National Weather Service Office's website.  To find this:


Go to the National Weather Service.
Click on your local area (which will take you to your local NWS Office webpage)
Scan across the middle of the page about halfway up to find the climate and past weather drop down and you should come across the NowData link (for this one I had to click more in the menu)


Disappointingly tough to navigate to the NowData hub, but you only really need to find it approximately once, and then you're set!

To speed you along: this is the direct link for the Atlanta (Peachtree City) area.

Then, once you get to the NowData page, you want:


The Atlanta area as the selected location (that will combine the past and current official Atlanta observation sites together to go back as far as possible for the official Atlanta observation)
For product, click the calendar day summaries radio button
The year range should likely be good... you want por- (por = period of record, meaning back to the very start of record keeping)
Variable = Precipitation
Summary = Daily Maximum


And viola, click Go, and you'll have it.  No, it's not a single list.  In some ways, to some, it may be better, it's a page of the maximum precipitation values every day of the year.  (Which allows you to see other things that might pique interest... such that [as is common in precipitation data due to such wild variability], the days calendar days on which Atlanta has never received an inch of rain are: February 29, April 21, May 10, May 12, September 9, September 12?

Anyways, it's a bunch of numbers... but the extra positive is that the maximums for each month are highlight red.  So just search through those quickly, you should find that the maximum 24-hour recorded rainfall in Atlanta history is:

1. 7.36" on March 29, 1886

Second (assuming there was no additional great storm on a different March 29th!) was much more recent:

2. 6.68" on October 4, 1995

You may well be able to dig around the climate category on that Peachtree City National Weather Service page and find more information on the major storms including those, and a better, simpler list.  But if not, at least the NowData offers the chance to reliably get answers to many questions like yours.

I know, it's definitely not all the most intuitive.  At least it's consistent.  And, especially if you have some rudimentary spreadsheet experience, it can be made to tell you what you need rather quickly (in 15 years of meteorology, I still regularly use it myself.)  If somebody has a very reliable, comprehensive source for historical data that is fairly straightforward to the typical user, I'd be absolutely right at the front of the line to congratulate them.

(And it is indeed a real pity, that in an era where the big concern is supposed to be changing climate, it still is fairly abstruse and convoluted to get great comprehensive climate information in an intuitive way from an official source)

But hopefully, while it's not absolutely beautiful in method, it not only answered your question, but given you and others the tool to answer the same question and quite a few others on temperature\precipitation climate\history for many other cities around the country!