Williams grew up in Altamonte Springs, Florida, and attended Lyman High School, where he played football for coach Bill Caughell.

In his junior year, Ian was responsible for 83 tackles, 23 tackles for loss (TFL), 12 hurries, 4 forced fumbles, 2 sacks, 4 fumble recoveries and 4 passes broken up, as the Greyhounds won their third straight 5A district title and beat Melbourne High School (Melbourne, Florida) for Lyman’s first Florida playoff win in school history.

Williams was heavily recruited, receiving scholarship offers from Notre Dame as well as most of the top southern programs in the country, including by Alabama, Auburn, Clemson, Florida, Mississippi, and South Carolina.

Not wanting to influence his decision, Natalie waited until after Ian signed with Notre Dame to tell her son of his grandmother's prescient forecast.

Prior to the injury, he was one of only two players to appear in every game of his four-year Notre Dame career (Kerry Neal is the other).

[7] On September 15, 2013, Williams broke his left ankle in a game against the Seattle Seahawks and was subsequently placed on injured reserve, effectively ending his season.

[8] On September 9, 2015, Williams was named a defensive team captain by head coach Jim Tomsula.