I will add also a link to the question on Mathematics Meta: Can you tell who created a tag. (Looking at the dates, it seems very likely that the query linked in the Glorfindel's answer was created by the answerer of this particular question.)
Sometimes you can find various related queries in MO editors' lounge. (MO editors' lounge was created by quid back in 2013. The intended purpose is to have a room related to tagging and editing.) For example, recently we looked at history of the tags (magma) and (magmas).
This is again by no means completely reliable, but creation of a new tag is sometimes mentioned in this chatroom. (At least the more recent instances.) Here are many examples of such messages. So, for example, you can search the room for messages containing the tag (technology) and you'll find out that there was a question on meta with this tag, but it was later removed by an automated script since it was used only on a single question for a long time. (This is done after 12 months on meta, 6 months on the main site. This script is another thing which makes finding the first occurrence of a specific tag from SEDE more difficult - since in instances like that, the tag is also removed from revision history. So no trace of such tags is left on the site or in SEDE.)