Each state maintains separate statutes that govern the specifics of how a married couple may obtain a divorce. In Illinois, the law recently converted to only recognizing "irreconcilable differences" as grounds for divorce. This simplifies the process in some ways and does away with antiquated grounds for divorce that were sometimes abused in modern contexts.
Now that Illinois is solely a "no-fault" state, outdated grounds for divorce like habitual drunkenness have been done away with. Instead, to obtain a divorce, you must only demonstrate that you and your spouse have been separated for at least six months. This is a significant change over the prior requirement of two years.
It is worth noting that demonstrating separation does not necessarily mean that you and your spouse have been living in separate places or under different roofs. There is legal precedent to establish that it is enough to demonstrate that you and your spouse have been living significantly separate lives for at least six months. Once you are able to demonstrate that you and your spouse have been effectively separated for at least six months, then you can effectively claim that you have met the requirements of irreconcilable differences.
Of course, meeting the legal grounds for divorce is only the beginning of a deceptively complex process, even in the most amicable of divorces. Divorce is, in the eyes of the law, as much a business relationship as an interpersonal one, and arriving at a fair division of assets that will be approved by a court can be trickier than you might expect. If you are considering a divorce, even one that is mutually amicable, it is wise to consider enlisting the guidance of an attorney to help you grasp the full scope of the issues at stake and keep your rights protected in the process.
Source: The News-Gazette, "John Roska: Illinois now a 'pure' no-fault divorce state," John Roska, Jan. 15, 2017