The 11,000-strong union made its decision after questioning the candidates about the issues.
For Chico, it is a huge endorsement.
"The reason that it is so important, about what we are talking about here today, is that it is the number one issue on the minds of voters in this city, and these are the men and women who provide that safety to our citizens," said Chico.
The city's dire financial situation is a big issue as well. And while Chico acknowledges the police force will have to make sacrifices, he refuses to talk about how the police union could help balance the budget.
"Here's where you get into the problem of collective bargaining. When you do things unilaterally. When you prejudge things as we have seen other candidates say," he said.
Chico was referring to Rahm Emanuel who has indicated that issues such as retirement age or employee contributions should be talked about as ways unions could sacrifice.
The FOP admits its membership voted for Chico over Emanuel by less than 100 votes.
Emanuel responded to the endorsement with his own plans to fight crime.
"I have a crime strategy of about putting more police on the street and about getting kids, guns and drugs off the street," said Emanuel.
Mayoral candidate Miguel del Valle is confident he will get votes officers, despite the Chico endorsement.
"I was one the one who brought back funding to establish blue-light cameras in all our high schools throughout the city of Chicago and surrounding areas. I am the one who has worked to improve the CAPS program," said Del Valle.
While candidates are getting endorsements almost daily from groups and people, mayoral candidate Carol Mosely Braun remains upset that former President Bill Clinton endorsed Emanuel.
"The African-American community stood by Bill Clinton when he had his toughest times with Monica Lewinsky and other issues. And For him to parachute into Chicago to support a candidate who probably does not live here is just bad," said Moseley Braun.