Probably used on a farm for grain.

From an article in the Chicago Tribune - "Before
the advent of refrigeration, crocks were used in American kitchens to
hold foodstuffs such as butter, salted meats and pickled vegetables. The
crocks were invariably made of stoneware, a durable, economical ceramic
that remains water-tight, even without a glaze."

From 'Homesteading Today' - "Crocks held butter, sugar, whole spices
from the grocer, flour, coffee, tea, honey, molasses, pickles, smoked
fish, smoked meats, etc. etc. if it could be cut up and packed it was
put in a crock for storage. There were also cheese crocks.
Jugs were obviously used for liquids..a gallon of honey and then they'd
pour that off into a small crock and keep the crock on the table or in
the kitchen cupboard..same with molasses..smaller jugs held daily or
weekly vinegar, herbal concoctions, oils, etc.
and don't forget the whiskey jugs. Gin (which was very popular) came in bottles, not jugs.

And crocks were used to store left overs too..crocks were put into ice
houses and running streams..they kept everything wonderfully cool.

If people wanted the food to be water-tight or airtight, they poured
paraffin wax over the top...Most "stored" food in crocks was already
processed by either pickling, smoking or salting though, so usually food
would simply be "wrapped" in a muslin covering to keep bugs away. Flour
& sugar crocks had lids."

The size is shown by the 4 on the crock, meaning this one would hold 4 gallons.