John Gill Commentary Numbers 26:63

"These are they that were numbered by Moses and Eleazar the priest, who numbered the children of Israel in the plains of Moab by the Jordan at Jericho." — Numbers 26:63 (ASV)

These are they that were numbered by Moses and Eleazar the
priest
That is, these were the Levites, their families, and the number of males in them, which was taken by Moses and Eleazar, who might be only concerned in numbering the Levites, of which tribe they were: and

who also numbered the children of Israel ;
all the tribes of them, with the assistance of their princes:

in the plains of Moab, by Jordan, near Jericho ;
as they were commanded by the Lord.