Indiana Code Title 6. Taxation § 6-5.5-6-1

Sec. 1. Annual returns with respect to the tax imposed by this article shall be made by every taxpayer:

However, taxpayer members of a unitary group are required to file only one (1) return covering all members of the unitary group.  The taxpayer member that files the return may be designated by the members of the unitary group pursuant to consents executed by each member.  Each taxpayer member of a unitary group is jointly and severally liable for the tax liability of all members of the unitary group.