If you had no business activity, no business income or expenses, you do not have to file business tax returns. However, the state of Wisconsin requires you file an annual report. You can do that with this link to the Wisconsin One Stop Business Portal.
If you are the sole owner of the LLC (single member LLC) you can file your business activity on Schedule C with your personal tax return.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"