Vintage 1920s "Essex Cap" winter knit hat. Dated 1926. Dark blue hat with a button strap under the chin. This is a small size, probably either a boys (or kids) or maybe a very petite woman. It can stretch up to about a 21" head size (which is about a US 6.5 or a EU 53 or size XS). The chin strap is also not very long, so it is more inline with a being child's hat.
There are several repairs, but it is in pretty good condition considering it's a 100 year old knit wool hat. I am unsure what the two buttons on the top front of the hat are for.