Chicago Public Schools now have until March 31 to compile a list of schools to close.
Gov. Pat Quinn signed the bill Friday afternoon following action this week by the Illinois General Assembly on various versions of the legislation.
The House passed a bill 84 to 28 Wednesday despite opposition from teachers and some community members. The Senate then passed a different version with a 57-0 vote.
State law required the district to announce by Saturday which schools it will close next year.
New schools CEO Barbara Byrd-Bennett said the district will use the extra time to get input from parents and community members and come up with a comprehensive plan.
Opponents, however, said the extension still doesn't provide enough time for a thorough vetting or to mount an opposition to any closing.
The Chicago Teaches Union is against all school closures.
The Associated Press contributed to this report.