Numbers 1:32
Of the children of Joseph, namely, of the children of Ephraim, by their generations, after their families, by the house of their fathers, according to the number of the names, from twenty years old and upward, all that were able to go forth to war;
Cross-reference
Numbers 2:18 gives the same Ephraim census (40,500) and leader, placing them west in the camp.
Numbers 26:37 is a later census of Ephraim, providing a parallel count of the same tribe.
Numbers 26:35-37 records Ephraim's later census (32,500) — a different number from the 40,500 here, same tribe new generation.
Genesis 46:20 records the birth of Ephraim and Manasseh to Joseph in Egypt — the origin of the tribe counted here.
Genesis 48:1-22 describes Jacob adopting Ephraim and Manasseh as his own, making them tribes — the basis for their inclusion in the census.
Deuteronomy 33:17 specifically mentions 'ten thousands of Ephraim' in Moses' blessing — directly relating to the large number in this census.
Genesis 48:5 states Jacob adopts Ephraim and Manasseh as his own sons, making them tribes — the legal basis for their separate listing.
Judges 1:22 records the house of Joseph (including Ephraim) fighting against Bethel — a later historical reference to the tribe counted here.