http://www.transitchicago.com/yellowline/#hours

Yellow Line route provides rapid transit train service between Dempster-Skokie and Howard (in Chicago), with connecting service to downtown Chicago via Purple Line Express or Red Line.

This line is also commonly known by its original, service name, the "Skokie Swift."

Hours of Operation
Weekdays:
Dempster-Skokie to Howard 5:00a-11:15p
Howard to Dempster-Skokie 4:45a-11:00p
    
Saturday:
Dempster-Skokie to Howard 6:30a-11:15p
Howard to Dempster-Skokie 6:15a-11:00p

Sunday/Holiday:
Dempster-Skokie to Howard  6:30a-11:15p
Howard to Dempster-Skokie 6:15a-11:00p