Hundreds of police officers waited outside the Midtown church and held a moment of silence as Rivera's casket was carried inside.
The wake came just hours after an emotional vigil for Rivera and his partner in Harlem.
Mayor Adams attended the wake, while a host of officials and members of the public stream in throughout the day.
Officer Rivera's remains were transferred from the Riverdale Funeral Home in Inwood Thursday morning ahead of the wake. A full processional was held from the funeral home to St. Patrick's Cathedral.
As Rivera's casket was wheeled into the cathedral and placed for his wake, his family -- including his wife of only four months, Dominique Rivera -- were escorted inside.
Wake held for fallen NYPD Officer Jason Rivera
The two were childhood friends and just married on Oct. 9. She penned a beautiful tribute to her late husband and called hi her first love.
NYPD officers were joined by everyday New Yorkers to mourn side by side.
"Police get up every morning put on their uniforms and kiss families goodbye without knowing if they're gonna come back that evening and these two officers didn't," said Steve Weiss who was paying his respects.
Rivera's funeral is scheduled for Friday at the cathedral.
The NYPD warned street closures will be in effect:
Last night, hundreds of people gathered outside the 32nd precinct in Harlem, where Officer Rivera and his partner, Officer Wilbert Mora, worked.
Show of support at vigil for fallen NYPD officers Rivera and Mora
A candlelight vigil remembered these two young officers, who were both murdered in the line of duty after being ambushed in the Harlem neighborhood they patrolled.
Fellow officers spoke out.
"These are two of the best individuals you could ask for," said NYPD Inspector Amir Yakatally. "These are the officers that we all are begging for. We lost a major part of the future last Friday. And it's only been a few days, and we have a lot of work to do, we have a lot of healing to do. It left a major hole in this precinct."
"I'm still hoping this is all a dream and I wake up tomorrow," said Officer Charles Reyes. "It's a nightmare, actually. And I get to speak to you one last time, and I get to say I'm sorry, I'm sorry for not being there."
"Your smile lit up a room, your smile changed everybody's mood," said Officer Sterling Medina.
The wake and funeral for Officer Mora are set for next Tuesday and Wednesday, also at St. Patrick's Cathedral.
The 27-year-old officer died Tuesday at NYU Langone Health in Kips Bay.
He was transferred there Sunday from Harlem Hospital where his organs were donated to five people.
JetBlue has announced it is providing free airfare to any members of law enforcement and public officials who are looking to attend Officer Mora's funeral next week.
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