Count of the number of editors for each month on the English Wikipedia.

Data taken from https://stats.wikimedia.org/#/en.wikipedia.org/contributing/editors/normal%7Ctable%7Call%7C~total%7Cmonthly.

See there for further details.
An "active" editor is one with 5 or more edits in that month.
Editors in each month for the English Wikipedia
Editors in each month for the English Wikipedia that are "active"
Editors in each month for the English Wikipedia — Total and "active"
Percentage of editors deemed "active" in each month for the English Wikipedia