Kenny was last season's Player of the Year after making a bargain-basement move from Bury, while Tonge has seen his many barnstorming performance and spectacular goals rewarded with England Under-21 recognition.
Neil Warnock was clearly pleased.
"I'm absolutely delighted that both have extended their contracts - we feel both deserve it having established themselves as key members of the first team squad.
"At Bramall Lane we have to look after our players as part of the family - that is the way forward for Sheffield United".
After re-signing Kenny and Tonge, Warnock will now start chasing Michael Brown's signature. Rumours have abounded recently that several big clubs, including Manchester City, Everton, Leeds and Rangers, have been tracking the midfielder.
Brown is free to sign a new contract from January, and the manager is keen to see the matter resolved.
"Michael knows we want him to stay and I don't see any reason why he cannot maintain his high standards over the next three or four years.
"I will be speaking to him after the Reading game because we finally have a blank week. The contract situation is in his hands, we have made him an offer and he is thinking about it."