Libraries in Buxton, Chapel-en-le-Frith, New Mills and Bakewell are among 25 across the county to have their opening hours revised.
Derbyshire County Council said the new times, although reduced, will ensure the libraries are open when most people regularly use them.
The move is expected to save the service £400,000.
Council leader Barry Lewis said: “These changes are an integral part of the overall Libraries for Derbyshire programme and have been worked out so that hours are reduced at each library’s quietest time, to cause minimum disruption to users.
“To ensure they remain as accessible as possible, all 25 county council libraries will keep a late night opening and will be open on Saturdays, with possible lunchtime opening for users’ convenience. We’ve also increased what people can do and access online and made it easier to join the service online too.”
As part of the Libraries for Derbyshire programme, 20 libraries are to be transferred over to community groups and organisations.
So far half of these, including Hayfield, Tideswell and Whaley Bridge, have had groups come forward with robust enough plans to take them on.
Click here to see the changes to library opening times.