It would be easy to find the legal data. All it takes is a quick search. The number of illegals would be much harder to determine, because the administrations that favored it hid the numbers as best they could.
I remember reading somewhere that between 750,000 and 1,000,000 people come here legally every year since the early 90s.
I'd agree with your 100 million estimate, factoring in the illegals. If anything, you're probably a bit low.
EDIT: I found this data(migrationpolicy.org) on legal immigration. I'd have to dig into it to see how reputable the source is.
I just asked grok. Based on info from Pew, DHS, Wikipedia, etc. here is the salient content of the response: my guess would be:
Legal immigrants: ~68 million (based on higher-end historical estimates). Illegal immigrants: ~20–30 million total entries, with maybe 10–15 million staying permanently. Adding the lower end of illegal entries (20 million) to 68 million legal immigrants gives ~88 million. Using the higher end (30 million) pushes it to ~98 million. Splitting the difference, I’d estimate around 90–95 million people have immigrated to the U.S., legally and illegally, since 1965.