US object identifiers are handed out by ANSI, the contact person is Michelle Maas <mmaas at ansi.org>
There is a second US branch of the OID tree, 1.2.840 (iso(1) member-bodies(16) usa(840)); some organizations are listed there, but new registrations are made under the 2.16.840 arc.
As of this writing, only 1 (companies), 101 and 102 (both US govt) are allocated under this branch.
See also the OID Repository website reference for 2.16.840