Galen Hekhuis wrote:

They are both of the same order: Odonata. Dragonflies are in the
suborder Anisoptera while damselflies are suborder Zygoptera. It
seems except for size and wing-folding there seems to be not a whole
lot oaf difference between them. The nymphs seem to exhibit the most
distinct differences.

I always distinguished between them by observing their eyes.
Dragonflies tend to have their eyes on the front of their heads.
Damselflies have them on the sides. I looked it up in the book
published by the Seattle Audobon society "Dragonflies of Washington" to
be sure.

Iduna