The $43 million station modernization effort included the Addison, Irving Park, Montrose, Harlem and Cumberland stations.
Some of the changes riders may notice include platform upgrades, more turnstiles and better lighting.
"The upgrades to these stations, which had a combined 5.5 million station entries last year, will provide a more pleasant customer environment and complement other Blue Line improvements that have enhanced service reliability and customer comfort," said CTA President Dorval Carter.
This is all part of a larger, four-year, $492 million Blue Line rehab project that will have 13 of the 16 stations on the O'Hare branch receiving makeovers.
On Sunday, the CTA announced $75 million in funding for an extension of the Red Line.