Folks on “Medicaid,” (Medi-Cal) in CA, are usually indigent (or close to it). Most of them are on SSD, SSI or TANF. When an individual is collecting SSD, I don’t believe they are allowed to have W-2 income. If they do, they can lose their SSD benefit. Thus, the majority of people on Medi-Cal are NOT required to file an income-tax return.
Persons incarcerated in state or Federal prison do not typically have income and thus would not be required to file an income tax return. This doesn’t preclude their non-incarcerated spouse to file one, however, but it likely wouldn’t be a “joint-return.”