He was the First Assistant United States Attorney of the Northern District of Illinois from 1971 to 1977.

[2] On June 2, 1980, Kocoras was nominated by President Jimmy Carter to a seat on the United States District Court for the Northern District of Illinois vacated by Judge Alfred Younges Kirkland Sr. Kocoras was confirmed by the United States Senate on September 29, 1980, and received his commission on September 30, 1980.

[2] Kocoras presided over the September 2006 suit brought by bulk email company e360 Insight against the anti-spam organization Spamhaus.

He awarded e360 a default judgement totaling $11.7m in damages,[3] an amount reduced to just $3 on appeal.

[4] In January 2014, Kocoras sentenced Ty Warner, the billionaire sole owner of Ty Inc. (maker of Beanie Babies and other plush toys), for failing to declare and pay income tax on earnings in a Swiss bank account.