From 2,997 active users across all lemmy instances at the beginning of June, the number increased to 52,797 by June 30th. Source.
An active user on Lemmy is "someone who has posted or commented on our instance or community within the last given time frame.” Source. That means lurkers are not counted as active users. There are currently almost 200k total users spread across the top 10 non-bot lemmy instances.
We're really building something here!
EDIT: Looking for a lemmy app? Here's a whole list: https://lemmy.world/post/465785
Until they ban NSFW content
Killing old.reddit will be big too
And probably coming relatively soon as it's much easier to scrape