Sorry to contradict you, Ian, but I think you've got it wrong.
Per Corpora (page 8 of http://www.sca.org/docs/govdocs.pdf)
are administrative groups, which may (or might not) have other groups
that report through them. That's it.
Historically, the way it's tended to work is that one group gets (or
starts out) big enough to be a Barony (25 people). As other groups
begin to emerge, they are fostered in their early years by that
bigger Baronial group (in similar fashion to how Foxvale has been
fostered by Tree-Girt-Sea). Sometimes, those emergent groups, on
being recognized as full-status, choose to remain part of the Barony
they "grew up" in, in which case they become Cantons.
So, sometimes a Barony will consist of a single group (in fact, this
is currently true of every Barony in Illinois). Other times, a
Barony may include Cantons, which report through the Barony
(Sternfeld is one such: most people around Indianapolis are residents
only of the Barony of Sternfeld, but those in Boone and Hendricks
Counties are ALSO members of the Canton of Qal 'at Ja'far). There's
nothing prohibiting any member of the Barony (including one who
resides in a Canton thereof) from serving in any Baronial office
(including that of Baron or Baroness), although it may be possible
for specific Baronial charters to specify differently.
More recently, it's been known to happen (both in the Midrealm and
elsewhere) that several existing groups throw their lot in together,
to form a Barony, in which no one group holds the same name as the
Barony itself-- that is, every Canton has its own identify, and are
co-equal partners in the Barony. This sort of collective has come to
be known as a "shell Barony" (notably, NO official document that I
could find, at the Kingdom nor Corporate level, uses this term). It
is not definitively different in any way from any other Barony.
So, for our purposes, the useful distinction is this: In choosing to
formally collectivize the local groups, we could either advance ANY
of those group to a Barony, and bring any of the other groups in as
Cantons thereof, or we could create some new administrative unit, and
make all of the groups Cantons of that. The latter case is what we
call a "shell Barony", and it's what I personally believe makes most
Of course, it's also possible for any of the groups that has 30
members and a full staff of officers to become a Barony, without any
of the others coming along. But, as I said some months ago in a TGS
meeting on the subject, "I think it's only worth Tree-Girt-Sea
becoming a Barony, if the purpose is to bind us to our neighbors."
Hope this helps!