Your date of last insurance is very important in Social Security Disability.
Social Security is an insurance program. In other words you must pay into Social Security to be eligible.
For example, if you work for a University in Illinois or you are an Illinois public school teacher you do not pay into Social Security. If you become disabled you may not be able to collect if you do not have enough quarters paid in. There are exception, of course. Such as someone who works a second job that contributes to Social Security.
To be eligible for Social Security disability your disability must have started before your date of last insurance.
You can find out your date of last insurance by calling your local Social Security office.
In the event your date of last insurance has lapsed you will only be eligible for SSI. The problem with SSI is that you are only eligible for approximately $670 per month, and most other income and assets reduce the amount you can receive.