I live in Ga but went to college in Illinois.Took a gap year working in Illinois pending Law school. Should I file as an Illinois resident or non resident?

Generally, it would appear you lived and worked in IL and would file an IL resident tax return and not a GA return.  However, it really depends on the circumstances (see the links below).  Since you ceased being a student and were in IL for employment purposes that would support being an IL resident and also supports not being a GA resident.  NOTE:  Since you worked in IL, IL will tax those employment wages in all situations.  

 IL says here,

 "The term "resident" is defined in IITA Section 1501(a)(20) to mean: 1) an individual who is in Illinois for other than a temporary or transitory purpose during the taxable year. "  

Further, "Presumption of residence and non-residence:   If an individual spends in the aggregate more than nine months of any taxable year in Illinois it will be presumed that he is a resident of Illinois."  

GA says here, 

"1. A Georgian resident for the entire current tax year shall be a natural person who has actually stayed in the territory of Georgia for 183 or more days in any continuous 12-calendar-month period ending in that tax year, or a natural person who was in a foreign country in the public service of Georgia during that tax year. 

2. The time of actual stay in the territory of Georgia shall be the time, during which a natural person stayed in Georgia, as well as the time he/she spent outside Georgia specifically for treatment, leisure, business trip or education."