The alleged cell had members in various parts of impoverished upper Egypt and was led by an “emir” Mostafa Ahmed Abdelaal.
The militants, charged in 2017, had “set up a terrorist cell in Upper Egypt which declared allegiance to (IS leader) Abu Bakr al-Baghdadi”, the court official said.
The court sentenced 18 of the defendants to life terms (25 years) and another 41 to 15-year prison terms.
It also handed six minors five years each in jail and acquitted two suspects.
The sentences can be appealed.
Since Egypt’s military toppled Islamist president Mohamed Morsi in 2014, the government and security forces have cracked down hard on secular opposition and Islamist extremism.
The Egyptian branch of IS has led an insurgency in North Sinai and carried out attacks across the country.
Egypt’s army launched a major offensive in February dubbed “Sinai 2018” to dislodge the insurgents from the peninsula.
More than 450 suspected jihadists and around 30 Egyptian soldiers have been killed since the offensive began, the army said in October.
Jihadist attacks in recent years have killed hundreds of police, soldiers and civilians.
IS claimed responsibility for an attack last week against Egyptian Christians in Minya province, which killed six Copts and one Anglican.
Egyptian courts have convicted many suspected jihadists in mass trials which have been criticised by human rights groups.
An Egyptian military court on Wednesday sentenced eight IS members to death for a deadly attack against the army in 2016, officials said.