Setting up a US company—whether an LLC  or a Corporation (C-Corp or S-Corp) —does not end once the state approves your formation documents. In practice, post-incorporation compliance  is where most founders face delays, banking rejections, tax notices, and operational risks. This guide provides a clear, authoritative checklist  covering what every new US company must complete after formation, including EIN registration, banking, internal agreements, tax setup, and ongoing com