We had a party after my son’s graduation this year, but it was mostly family. A few families have larger parties, but I think there aren’t that many, and most of them are “hubs” with friends all having one party together at one kid’s house. Not a big thing.
Our school also does a Grad Night party each year where we rent out a big Water Park with crazy slides, a wave pool, two mini-golf courses, full arcade, and laser tag. The party is fully catered, and starts at 8 or 9 at night, and goes until 4am. It’s a “keep the kids sober” deal, and it attracts close to half the graduating class, I think.
We are going to have a bigger party later when my son returns from Europe where he is spending about 7 weeks this summer, and before he leaves for USC.