What is the collective noun for wagons?

There isn't a widely accepted collective noun specifically for wagons. However, you could use these options:

General terms:

* A train of wagons

* A fleet of wagons

* A convoy of wagons

* A line of wagons

* A string of wagons

More specific terms (depending on the type of wagon):

* A team of covered wagons (if referring to pioneer wagons)

* A stable of horse-drawn wagons

* A collection of toy wagons

The best choice will depend on the context of your writing.