He is 5-foot something, 100-and-something pounds.

He didn’t start lining up at wide receiver until his third season at Illinois. He went undrafted. Then, less than two months into his second NFL season, he was cut for the third time.

Isaiah Williams was repeatedly told what the world thought of his dream.

“When you go through all these things, you go through being cut, you go through people telling you you’re not good enough, you’re not this, you’re too small, you’re too slow … I used to focus so much about what people thought about me and the box they put me in,” Williams said following Monday’s Jets practice. “There have been some moments in my NFL career — one being last year — it hurt a lot.”

On Oct. 4, the Jets released Williams — who had been signed off the Bengals practice squad less than a month earlier — after he fumbled a kickoff and called for a fair catch at the 3-yard line during a loss in Miami. 

By the end of last season, Jets players voted him the team MVP after he returned two punts for touchdowns while averaging 14.1 yards per punt return and 30.2 yards per kick return.

“Players like that demand respect and demand reps,” head coach Aaron Glenn said recently. “What makes him such a special player is that there are so many things he can do on offense. We’ve got to give him the ball and make sure he’s involved because he’s an explosive player.”

Williams, 25, is creating more opportunities for himself with a strong training camp, gaining the inside track for the Jets’ No. 3 receiver spot — ahead of first-round pick Omar Cooper Jr. — after starting the preseason opener against the Buccaneers.

Last week, Jets wide receivers coach Shawn Jefferson described Williams as “a heartbeat on offense.”

“If I was in a burning building, boop, boop, boop,” Jefferson said while mimicking dialing a phone. “‘Hey I need you to come to get me,’ he’s on the way. I literally watched this kid at death’s door. And just how he had the mental fortitude to just fight back … When you’re down, you’re not out. Just keep going, keep pushing.”

In addition to his returning duties last season, Williams had 26 catches for 193 yards — and three carries for 34 yards — offering optimism that he could make a greater impact with more playing time this season.

But it doesn’t matter what anyone says.

“As guys see that you’re dependable and they can trust you, more is gonna come,” Williams said. “Whatever my role is, I want to be a master at it. And if you do that, all the glory will come.

“Being around so many teams, I had the opportunity to learn from so many guys. Watching how Garrett [Wilson] operates, being around [Detroit’s Amon-Ra] St. Brown … Ja’Marr Chase, Tee Higgins, I’ve always been observant. Everything they did, I was just watching. What makes him great? Being around all these top receivers, a lot of them are special, but a lot of them are just consistent … … After a while you watch and you learn from other guys, and be like, ‘OK, I know exactly how to last in this league.’ ”