The judge's order applies to migrants who were subject to warrantless arrests that took place without probable cause, according to the Chicago Tribune.
The newspaper said the judge would allow detainees to be released on $1,500 bond with some form of monitoring, including electronic ankle bracelets.
The detainees were among thousands of migrants arrested during immigration raids in the Chicago area dubbed "Operation Midway Blitz." Many of those taken into custody have already been deported or agreed to leave the country voluntarily.
The Department of Homeland Security (DHS) condemned the judge's ruling in a post on X.
"At every turn activist judges, sanctuary politicians, and violent rioters have actively tried to prevent our law enforcement officers from arresting and removing the worst of the worst," DHS said.
"Now an ACTIVIST JUDGE is putting the lives of Americans directly at risk by ordering 615 illegal aliens be released into the community."
The judge's ruling came in response to a lawsuit filed by the National Immigrant Justice Center and the American Civil Liberties Union which alleged the wave of migrant arrests were unlawful.
The decision is the latest setback to President Donald Trump's immigration crackdown in Chicago, America's third-largest city.
Trump has ordered hundreds of National Guard troops to the Democratic-run city to combat crime and aid immigration efforts but the deployment has been blocked by federal courts.
The Trump administration asked the Supreme Court last month to lift the lower court rulings blocking the deployment of the National Guard in Chicago.
The Republican president has sent National Guard troops to three Democratic-led cities this year -- Los Angeles, Washington and Memphis -- but his efforts to deploy soldiers in Portland and Chicago have been tied up in the courts.
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