The senator, who was the Republican nominee for president in 2008, announced on Wednesday announced he had been diagnosed with brain cancer Wednesday.
Rep. Nita Lowey (D-Harrison) said she was deeply saddened to hear of McCain's diagnosis.
"He is a true public servant and an American hero," Lowey said. "He's also a fighter, and my heart is with him as he begins this fight. I will keep him and the entire McCain family in my prayers.
Rep. Sean Patrick Maloney (D-Cold Spring) said the news was just "terrible."
"John McCain is a respected colleague and American hero who served our country during the Vietnam War," Maloney said. "I know he will fight this with everything he has. Thinking of him and his family tonight.
Rep. Eliot Engel (D-Bronx) said McCain was tough as they come.
"There's no doubt he'll face this challenge with the courage and strength that have defined him across five decades of public service," Engel said. "My thoughts are with him, Cindy and the rest of the McCain family."
Rep. John Faso (R-Kinderhook) said McCain was a patriot with a legacy of service and sacrifice and he was praying for his full recovery.
Dutchess County Executive Marc Molinaro met McCain in 2006, admitting he was thrilled and starstruck to meet the senator.
"We spoke for only a moment, he put his hand on the side of my head and told me to stay in politics, 'We need young people passionate about service.'"
Later when McCain was giving a speech about service, he asked Molinaro to stand and thanked him for his service.
"It was a humbling honor I will never forget," Molinaro said. "For his service and sacrifice, we are all grateful. For his speedy & full recovery, we pray."
Click here to follow Daily Voice Poughkeepsie and receive free news updates.