It's part of util-linux, but Debian has packaged it in the bsdutils package. There's a pile of other packages that are also compiled from the util-linux source package, apart from `util-linux` and `bsdutils`.
You can see the (installed) binary package a file belongs to with `dpkg -S`:
$ dpkg -S /usr/bin/logger
bsdutils: /usr/bin/logger
`apt-cache showsrc _package_` should show the corresponding source package, but I just looked at the online package search; the source package is mentioned in the side bar.