I've updated a few charts that look at the number of priests and members of religious orders over the last several decades. To avoid it looking like spaghetti, I only used the top dozen orders based on number of priests*. I also split the top 4 from the other 8 - there is very little overlap between the two sets and it makes the charts much clearer.
The charts are posted here. (.pdf format)
The Jesuits were the first order (of the top dozen) to have lost more than half of their members from their recent high point (from 36,038 in 1966 to 17,908 in 2011). They are currently at 15,591 members, down 57% from the all time high.
One might note that there is no significant change since Pope Francis (a Jesuit) became Pope. In fairness, it normally takes several years for any event in a religious order (or diocese) to have an impact on the vocation numbers.
Two more orders reached that milestone in 2016: Franciscans (now down 52%) and Oblates of Mary Immaculate (now down 52%).
Two more orders are very close to reaching that point: Redemptorists (down 47%) and Vincentians/Lazarists (down 43%). Both showed a small drop in the last year.
In terms of priests, only one order has reached that point, the Benedictines which are down 52% from their recent high point (from 7,058 in the early 1970s to 3,420 in 2019).
Three other orders are in danger of reaching that point: the Oblates of Mary Immaculate (down 49%), Jesuits (down 47%), and the Franciscans (down 46%).
In the top dozen, only one order, Divine Word Missionaries, has hit its high mark in terms of members in recent years (6,131 in 2009).
In terms of priests, two orders hit their highest mark in 2016: Divine Word Missionaries with 4,231 and Discalced Carmelites with 2,937.
The Benedictines had the best year of the top 12, increasing their number of priests by 6 and members by 184.
Overall, adding all of the top 12 together, the all time high was in 1966 with 160,926 total members. In 2019, that had dropped 42% to 93,214. In terms of priests, the high was in 1971 with 95,411 total priests. In 2019, that had dropped 33% to 64,119.
If current trends continue, the Jesuits will lose the title of largest religious order to the Salesians of Saint John Bosco. First by the number of members (4 years) and later by number of priests (11 years).
(* Out of curiosity I checked the top dozen orders based on number of members - it was the same dozen, but in a slightly different order.)
Note that only Male Religious Orders were included because that happens to be the data I have readily available. As time permits, I hope to do similar charts for Female Religious Orders.