Indiana's open container law is in Section 9-30-15-3 (b) of the Indiana Code.
(b) A person in a motor vehicle who, while the motor vehicle is in
operation or while the motor vehicle is located on the right-of-way of
a public highway, possesses a container:
(1) that has been opened;
(2) that has a broken seal; or
(3) from which some of the contents have been removed;
in the passenger compartment of the motor vehicle commits a Class C
infraction.
The trunk of a car is not part of the passenger compartment, so alcohol in the trunk will not violate this law.
Paragraph (a) of the law gives some other exceptions and clarifications, for situations like RVs, limos, and vehicles that don't have a trunk.