Issue the command:

dpkg -L package_name

If you are not sure which package installed a file, dpkg -S may be able to tell you. For example:

dpkg -S /etc/host.conf 
base-files: /etc/host.conf

The output shows that the /etc/host.conf belongs to the base-files package.

NOTE: Many files are automatically generated during the package install process, and even though they are on the filesystem, dpkg -S may not know which package they belong to.