ILKESTON, Sandiacre and Long Eaton libraries have had their opening hours slashed as part of the cuts.
Derbyshire County Council is making the changes to save £1.76m from its cultural and community services department.
Ilkeston Library in Market Place will close for four hours more a week – no longer opening on Mondays and Fridays between 5pm and 7pm.
Sandiacre Library will close three hours on Wednesdays from 2pm to 5pm and Long Eaton Library will shut for two hours on Mondays from 5pm to 7pm.
The decision was made by the council’s cabinet on Tuesday.
A council spokesman said: “The county council has to save £90m over the next four years and our libraries have to contribute to these savings.”