According to Nielsen ratings, about 23.1 million viewers tuned in to see to watch their favorite comedians, actors and musicians reunite at Rockefeller Center's Studio 8H.
The 3 1/2-hour show was NBC's most-watched prime-time entertainment telecast, excluding post-Super Bowl programs, in over 10 years.
In the key 18-to-49-year-old demographic, the special posted a rating of 7.8, making it the network's top-rated telecast in that demo since the "Will & Grace" finale in May 2006.
The special also generated lots of buzz (and laughs) on social media: Nielsen Social reported that a total of 9.1 million people in the U.S. saw the approximately 1.3 million tweets from more than 449,000 people in connection with the "SNL" special.
The show also delivered 188 million Twitter TV impressions, the highest of any series episode to date, according to Nielsen Social.
Some of the "SNL" guests -- including Justin Timberlake,
The New York-based firm uses relevant tweets, as measured by Nielsen, to gauge what emotions or "reactions" people have about TV. It found roughly 63% of the "reaction" tweets utilized the hashtag "#SNL40."
NBC's red-carpet coverage, which aired before the special, also scored big, with 11.1 million viewers total and a rating of 3.0 in the key demo.