All the events recorded in the Book of Numbers took place around eleven months after the Israelites arrived at the foot of Mount Sinai. The book itself is appropriately named Numbers because within it there is a lot of counting.
There are three censuses’ recorded in the Pentateuch, the first one is recorded when Israel was at Mount Sinai, and a census was taken to organise the Israelite families in order to establish a regular support for the Levitical priesthood, Exodus 30:11-16.
The second census was taken before departing from Mount Sinai in order to count the military men of the nation, Numbers 1-4. And finally, the third census was taken just before Israel entered Canaan, Numbers 26.