One of the victims, Russell Beyer, was a mold operator at Henry Pratt, where he also served as the union chairman, according to the company.
“My brother Russell was an amazing person. We all have holes in our hearts. He is sorely missed!” Beyer’s sister, Dawn, wrote in a comment on a Facebook post commemorating him.
Another was Vicente Juarez, the company’s stock room attendant and fork lift operator who worked at the company for 15 years, according the Chicago Sun-Times.
Juarez's son's girlfriend posted on Facebook that their "world has been completely turned upside-down."
In a GoFundMe set up to cover funeral arrangements for Juarez, his family said he was "a husband, father, grandfather, brother, son, uncle, cousin" whose "family depended on him extensively."
In a video interview with The Chicago Sun-Times, Juarez's daughter, Diana, wept and criticized the company for not reaching out to her family after the tragedy.
"Have they gave us a call? Nope," she said. "Have they said sorry, we're here, anything, whatever you guys need? Nope."
Another victim, Trevor Wehner, was a 21-year-old human resources intern just starting his first day at the company. He had been sitting in on the gunman's termination meeting according to Cindy Fuller, a family friend who paid tribute to him on Facebook.
"Each and every one of us have had a 'first day' on the job," she wrote. "His should have never ended this way."
Wehner's younger brother, Thomas, said he'll "miss being that annoying little brother to you."
"I love you so much bro. I remember all the times we would fight but no matter what happened I still loved you," Thomas posted on Facebook. "Rest easy big bro. I’m so proud of you."
His girlfriend, Winter Lane, remembered him as her "best friend and biggest supporter through the last three and a half years."
"I would not be where I am today without your wise words and warms hugs," she wrote on Instagram.
Wehner was supposed to graduate in May from Northern Illinois University, the same school where another victim, Clayton Parks, was an alumnus.
Parks graduated from the school's College of Business in 2014 and worked as the company's human resources manager.
"Loss like this is devastating and senseless," NIU President Lisa Freeman wrote in a note on Facebook. "I ask our university community to please keep the Wehner and Parks families, friends and communities in your hearts and offer them caring thoughts."
Parks was married and had a baby son.
In a Facebook post, his wife, Abby, called him "my husband, my love, my best friend, and the incredible father of our sweet son."
"Every time I’ve closed my eyes over the last twelve hours, I’ve opened them hoping to wake from a terrible dream, but that’s not the case," she wrote. "I’m living my worst nightmare."
"Beneath all the fog and the shock, and the crushing pain, I believe the same God that brought us together and gave us our precious son will somehow carry us through," she wrote.
Josh Pinkard, another one of the victims, was the plant manager at the company.
His family shared a photo with WVTM 13 in Alabama, his home state.
Pinkard "was a loving husband and a father who deeply impacted the community," his uncle told the station.
His cousin, Amy Pinkard Haynes, shared in a Facebook post that Pinkard had lost his younger sister, Kateah, 12 years ago in an accident.
"Last night he got his wings but Kateah got her brother back," Haynes wrote. "For that we take comfort in knowing there was a reunion unlike any we will ever experience on earth."
This is a developing story. More information on the victims will be added as it becomes available.