On the heels of Matt Leichter's recent work on law school faculty sizes, I looked at some of the data myself. I limited myself to 2011 to the present, because that's the only data disclosed by the ABA in a usable format. (Older 509 data is available but is bound in isolated PDFs until some good soul helps liberate it.)
Adding to the complexity are methodological changes by the ABA. It used to separate "full-time" tenured and tenure-track faculty from "other full-time" faculty, such as clinicians. In 2014, it did not separate those categories, but it also yielded a fairly significant one-year decline in that category, suggesting confusion or misreporting of data. And further adding to the complexity are seemingly-random fluctuations in faculty sizes from year to year, or stark differences between fall and spring terms, likely because the data is not serious accounted for and leaves errors.
For each year, I averaged the faculty sizes of the reported fall and spring terms among the ABA data, excluding the Puerto Rico schools. Full-time faculty (including "others" before 2014) declined from 9,028 in 2011 to 7,932 in 2015, almost a 14% decline in four years. That is hardly surprising. Part-time faculty, including adjuncts, remained fairly flat, hovering around 9,100.
But "deans, librarians, and other who teach"? It's a somewhat nebulous category, identified by one recent ABA key as "law school administrators who teach at least half-time. Administrators who neither teach nor hold faculty rank are not included in these numbers. Administrators who teach are typically at the school and available to students during the entire year." It's this category that's seen a 16% increase, from 1,752 personnel in 2011 to 2,032 in 2015.
Averaged out, the typical law school has lost about five faculty in the last four years, but the typical law school has also gained a teaching administrator or two in that same period.
UPDATE: A few have wondered whether it's a terribly useful consideration as the category includes "librarians." True, but recall that the definition extends to "administrators who teach at least half-time." Librarians who do not teach at least half-time would not be included. But I suppose it's possible that one could conclude that there has been a surge in law librarians as part-time faculty in the last few years.
UPDATE: Several commenters have offered alternative inferences to be derived from the data. I encourage you to consider their thoughtful perspective.