I live in one state, but drive across the border every day to work in a different state. What marketplace should I use to buy coverage?

You should buy coverage in the marketplace in the state where you live. In order to meet marketplace residency requirements, you must live in the service area of the marketplace. This means you 1) live in the state and 2) have the intent to reside there (even if you don't have a fixed address) or have a job or are looking for a job. (45 C.F.R. § 155.305 (a)(3)); CMS, FAQs on the Marketplace Residency Requirement and the Special Enrollment Period due to a Permanent Move, Jan. 19, 2016).