If you are a full year resident of Illinois and are filing a resident return, then, yes, you do have to report all of your income regardless of where it was earned.
If you are a part-year resident of Illinois then you would report all income earned while a resident of Illinois. So if you earned income in Washington during the time your were an Illinois resident it is taxable to Illinois. If you earned income in Washington while you were not a resident of Illinois you do not need to report the income to Illinois. In this case you would file a part-year resident or a nonresident return with Illinois. This type of return will allow you to allocate your income based on your residency at the time you earned the income.
