The registration of the Levites totaled 23,000, every male a month old or more; they were not numbered among the other Israelites, because no inheritance was given to them among the Israelites.
Levi was God's tribe, exempt from the land-lot and the war-muster, so the Levites escaped the curse that barred all others numbered at Sinai from entering Canaan. Yet their increase was paltry, only 1000 more, making them still one of the smallest tribes. Their losses to divine judgment were a lesson to all Israel.
AI summary
Commenting on Numbers 26:57-62
twenty and three thousand--so that there was an increase of a thousand (Num 3:39). males from a month old and upward--(See on Num 3:14).
Num 26:62 The Levites were not mustered along with the rest of the tribes of Israel, because the mustering took place with especial reference to the conquest of Canaan, and the Levites were not to receive any territory as a tribe (see at Num 18:20).