After the release of iOS 9 and OS X El Capitan I've been asked a few times if it was possible to transfer content from Evernote into Apple's revamped Notes app. And up until recently, I didn't think it was.
Then I stumbled upon this post on Yahoo Tech, where David Pogue walks through his reasons for ditching Evernote for Apple Notes. Buried about half-way down, he links to a free OS X app made specifically to transfer content from the Evernote app to your Notes account.
The process is really simple: After going through and highlighting notes in the Evernote app, you open the script and click the Play button. You'll be asked to confirm you want to move the notes over. A few seconds -- or minutes -- depending on how large of a move it is, an alert will let you know the process has completed.
Be sure to run the script titled "Export Evernotes notes to Apple Notes" and not "Delete All Notes." The latter option will delete everything from your Apple Notes account.
I tested it out with a handful of notes and it worked without issue. Pogue states he moved 1,400 notes over with success. However, the developer reports he ran into an issue where his Notes database become corrupted after using the tool. Your results may vary.