user659: Where can I find the blockchain, wallet.dat, etc. on each of the operating systems Bitcoin-Qt supports?

user22931: On windows8, the data folder is here: 
C:\Users\ ... your user name ...\AppData\Roaming\Bitcoin\

user38618: @ThePiachu is right

Linux:
~/.bitcoin/
macOS:
~/Library/Application Support/Bitcoin/
Windows:
%APPDATA%\Bitcoin

But since there are no instructions, it may be hard for a user to find them, so I'm going to add instructions.
macOS
1) Click the Finder symbol

2) Press command (cmd) ⌘ + option (alt) ⌥ + G at the same time.
3) Paste this into the window that opens:
~/Library/Application Support/Bitcoin/


4) Press "Go"
5) That's your Bitcoin folder!
Windows
1) Choose one of your folders, and open it (we won't do anything with the folder, so it doesn't matter if it's very important for you).
2) Click the folder icon next to the file location.

3) Paste the following:
%APPDATA%\Bitcoin

4) Press Enter ⏎
5) That's your Bitcoin folder!

user1674: On the new Mac OS X you can't see the Bitcoin folder in the library under /application support/. You have to use Finder and in the menu look for GO and then GO TO type ~/Library in the box. After that you can see the Bitcoin folder under /application support/.
Or you can hold down the Option key while selecting the Go menu and Library will become an option.

user323: It is the same data folder as the non-QT version of the standard client used to use:
Linux:
~/.bitcoin/
MacOS:
~/Library/Application Support/Bitcoin/
Windows:
%APPDATA%\Bitcoin
(This defaults to C:\Documents and Settings\YourUserName\Application data\Bitcoin on Windows XP and to C:\Users\YourUserName\Appdata\Roaming\Bitcoin on Windows Vista, 7, 8, and 10.)

659: <p>Where can I find the blockchain, wallet.dat, etc. on each of the operating systems <a href="https://en.bitcoin.it/wiki/Bitcoin-Qt">Bitcoin-Qt</a> supports?</p>
 22931: <p>On windows8, the data folder is here: </p>

<p>C:\Users\ ... your user name ...\AppData\Roaming\Bitcoin\</p>
 38618: <p><a href="https://bitcoin.stackexchange.com/users/323/thepiachu">@ThePiachu</a> is right</p>

<blockquote>
  <p><strong>Linux:</strong></p>
  
  <p><code>~/.bitcoin/</code></p>
  
  <p><strong>macOS:</strong></p>
  
  <p><code>~/Library/Application Support/Bitcoin/</code></p>
  
  <p><strong>Windows:</strong></p>
  
  <p><code>%APPDATA%\Bitcoin</code></p>
</blockquote>

<p>But since there are no instructions, it may be hard for a user to find them, so I'm going to add instructions.</p>

<h1>macOS</h1>

<p>1) Click the Finder symbol</p>

<p><img src="https://i.stack.imgur.com/9nads.gif" alt=""></p>

<p>2) Press <kbd>command (cmd) ⌘</kbd> + <kbd>option (alt) ⌥</kbd> + <kbd>G</kbd> at the same time.</p>

<p>3) Paste this into the window that opens:</p>

<pre><code>~/Library/Application Support/Bitcoin/
</code></pre>

<p><img src="https://i.stack.imgur.com/TRe4R.png" alt=""></p>

<p>4) Press "Go"</p>

<p>5) That's your Bitcoin folder!</p>

<h1>Windows</h1>

<p>1) Choose one of your folders, and open it (we won't do anything with the folder, so it doesn't matter if it's very important for you).</p>

<p>2) Click the folder icon next to the file location.</p>

<p><img src="https://i.stack.imgur.com/CC4he.png" alt=""></p>

<p>3) Paste the following:</p>

<pre><code>%APPDATA%\Bitcoin
</code></pre>

<p>4) Press <kbd>Enter ⏎</kbd></p>

<p>5) That's your Bitcoin folder!</p>
 1674: <p>On the new Mac&nbsp;OS&nbsp;X you can't see the Bitcoin folder in the library under /application support/. You have to use Finder and in the menu look for GO and then GO TO type <code>~/Library</code> in the box. After that you can see the Bitcoin folder under /application support/.</p>

<p>Or you can hold down the <kbd>Option</kbd> key while selecting the <em>Go</em> menu and <em>Library</em> will become an option.</p>
 323: <p>It is the same <a href="https://en.bitcoin.it/wiki/Data_directory" rel="noreferrer">data folder</a> as the non-QT version of the standard client used to use:</p>

<p><strong>Linux:</strong></p>

<p><code>~/.bitcoin/</code></p>

<p><strong>MacOS:</strong></p>

<p><code>~/Library/Application Support/Bitcoin/</code></p>

<p><strong>Windows:</strong></p>

<p><code>%APPDATA%\Bitcoin</code></p>

<p>(This defaults to <code>C:\Documents and Settings\YourUserName\Application data\Bitcoin</code> on Windows XP and to <code>C:\Users\YourUserName\Appdata\Roaming\Bitcoin</code> on Windows Vista, 7, 8, and 10.)</p>
