John Gill Commentary Numbers 2:19

"And his host, and those that were numbered of them, were forty thousand and five hundred." — Numbers 2:19 (ASV)

And his host
That is, the host of Ephraim;

and those that were numbered of them, [were] forty thousand and five
hundred .
40,500 men. Not his camp, but his host, or the army, which consisted only of his own tribe see (Numbers 1:33) .