The spokeswoman for Illinois Senate President John Cullerton confirms that the senate secretary has received Hendon's letter of resignation.
Hendon offers no reason for his departure in the letter. He denied having any "problems" with the federal government when speaking with ABC7's Charles Thomas.
He has served as senator for the 5th District since 1993. Before then Hendon worked in city and county government.
Hendon was not at his West Side office Thursday and before locking up, his staff had nothing to say.
U.S. Rep. Danny Davis says his long time friend and political ally broke the news to him over lunch.
"I was stunned. I was shocked. I couldn't believe it," said Davis.
Davis says Hendon was dismayed over the results of Tuesday's election, especially the defeat of city clerk candidate Patricia Horton whom he backed.
"He just couldn't imagine the turnout and the fact that people did not turn out to vote and that he was filled with anxiety, with remorse," said Davis.
Hendon's time in office has not been without controversy.
In October of last year, Hendon was criticized for calling gubernatorial candidate Bill Brady racist, sexist and homophobic. A week later, a court subpoenaed grant records related to programs that Hendon sponsored.
Hendon once called himself the black Sarah Palin, a reference, he said, to his African-American grassroots support.
Hendon had been a candidate in the race to become Chicago's mayor, but he dropped out in November. He denied the controversies had anything to do with his decision to leave the race, citing the need for the African-American community to rally around a single candidate.
"The community would always think he was trying to look out...and provide some assistance in terms of funding for different programs and helping their churches, and so most people would see he did a fairly decent job," said Alderman Emma Mitts, 37th Ward.
But not everyone agrees.
AmySue Mertens lost a primary race to Hendon in 2008.
"The people in the area where they needed it the most were not seeing the benefits of those funds," said Mertens.
Last year, Hendon came out with a book entitled "Backstabbers" about the perils of political office. After declining an interview request with ABC7, he said he was coming out with another book called "Backstabbers II."