According to the file hierarchy standard, /usr contains shareable, read-only data. So if the users should be able to modify the data, this is not the right location.
I would put it in /home/public or in /srv/public. Since the data is for all users, it may be placed in /home. If you plan to serve the data also on the network for other users I would place it somewhere in /srv.
To prevent that users may delete data from other users I would chmod 1770 the directory and chown it to root:data so that only users that are in the data group have access to this shared data.