Back on October 19, 2015, the Tip of the Night described a method to dedupe strings in a column of text using a RegEx search in NotePad ++. Here's an alternative method to use in NotePad ++ which doesn't require running a RegeEx. Catherine Wilhelm send posted the following solution on her blog.

Paste the column of data you want to dedupe in NotePad ++. Press CTRL + A to select all of the data. Then in the TextFX . . . TextFX Tools menu confirm that that T: +Sort outputs only UNIQUE (at column) lines is checked off.

Then simply click on T: Sort lines case insensitive (at column), and you'll get a column of deduped strings.