"On My Mac" folder disappeared from Notes, also cannot create notes unless iCloud is active

The On My Mac category is inaccessible if you store notes on one or more network servers, such as iCloud, and there are none stored locally.

In the Internet Accounts preference pane, disable all Notes synchronization by unchecking the corresponding box in all mail accounts with which you now sync. The data should be retained on the servers, but it would be wise to back it up anyway by following the instructions in this support article.

Quit and relaunch Notes. The database will be empty. Create a new note. From the View menu, select

Show Folders List

if the list isn't already showing. You should now see On My Mac. Re-enable synchronization. Relaunch Notes again. Your synced notes should reappear.

Try a restart.

Do a backup, using either Time Machine or a cloning program, to ensure files/data can be recovered. Two backups are better than one.

Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.

Isolating an issue by using another user account

If the problem is still there, try booting into the Safe Mode using your normal account. Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer. For each disable/delete, you will need to restart if you don't do them all at once.

Safe Mode - About

Safe Mode - Yosemite

Back up all data before proceeding.

Triple-click anywhere in the line below on this page to select it:

~/Library/Containers/com.apple.Notes

Right-click or control-click the line and select

Services ▹ Reveal in Finder (or just Reveal)

from the contextual menu.* A folder should open with an item selected. Quit the application if it's running. Move the selected item to the Trash. Relaunch the application and test.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.