What are the visa & residency requirements in Illinois?

"To visit or stay for an extended period in Illinois, visitors must apply for a visa or a green card, depending on the purpose of their visit. To apply for a visa, applicants must fill out a form with their passport details and flight itinerary. They must also a bring a letter of invitation from a U.S. citizen, a filing fee, several passport-style photographs, and any other documents required by the specific visa category. To apply for residency in Illinois, applicants must fill out an application for permanent residence, provide evidence of legal admission to the United States, and send in all of the required supporting documents. Applicants must also submit biometric data, such as fingerprints and a photograph, to the U.S. Citizenship and Immigration Services. Applicants may also have to attend an interview and take a medical examination before residency is granted," remarked another expat in Illinois.