headcount

Headcount is singular in spite of how many heads counted. Each individual headcount of multiple counted heads, that may or may not be a record count, would be part of the record. So long as head-counting is made a part of the record.

Your first language is UK or US?

Then what should I say to refer to the number of times recorded of people crossing checkpoints?

Your first language is UK or US?

Then what should I say to refer to the number of times recorded of people crossing checkpoints?

people

NEITHER American nor English use the word that way.

My sentence:
-This morning 100,000 headcounts are recorded crossing the checkpoint.


-This morning 100,000 people have been recorded crossing the checkpoint.

No, no, PEOPLE and PEOPLE FREQUENCY/HEADCOUNT are different.

If there are 3 people, then: Peter, Paul, and John.

If there are 3 people frequency/headcount(s), they could be Peter, Paul, and John crossing the checkpoint; they could be Peter crossing the checkpoint twice, Paul once, John none, and in this case there are two people crossing, but 3 people frequency/headcount. But I don't know the correct name and structure of using the term.

In that case, you might want to say two individuals/people crossed the checkpoint, but if you want to account for John, who didn't, you're just going to have to explain it every time. Are you looking for one word that accounts for one person crossing twice?

Is this what you mean -

This morning 100,000 crossings were recorded at the checkpoint.

It seems so; is UK or UK your first language?

There may be situations where that distinction actually matters, WB, and in that case specific jargon might have been developed to describe those differences.