The Bills announced just before midnight that newly promoted president Russ Brandon and his top executives also interviewed Oregon's Chip Kelly, one of college football's hottest prospects, and Syracuse coach Doug Marrone.
The Bills, stationed in Arizona for much of this week, didn't provide details regarding where the interviews took place or how long they lasted.
Next up for Buffalo is a trip to Denver on Saturday, when the team is scheduled to interview Broncos offensive coordinator Mike McCoy, according to a person familiar with Buffalo's plans.
The Bills are in the midst of their fifth coaching search since 2001 after Chan Gailey was fired on Monday.
It was a busy day for Kelly, as well. He also interviewed with Cleveland on Friday. Kelly's interviews were conducted a day after he led the fifth-ranked Ducks (12-1) to a 35-17 victory over No. 7 Kansas State in the Fiesta Bowl in Arizona.
Following the win, the 49-year-old Kelly said he wanted to get the interview process over "quickly."
The Bills are coming off their second consecutive 6-10 season and have not enjoyed a winning record since a 9-7 finish in 2004. They own the NFL's longest active playoff drought that's now at 13 consecutive seasons.
Buffalo has already interviewed former Cardinals coach Ken Whisenhunt, who was fired on Monday, as well as Cardinals defensive coordinator Ray Horton.
The Bills' meeting with Smith did not come as a surprise. Several reports surfaced over the past few days that the former Bears coach was interested in the Buffalo job since he was fired by the Bears on Monday.
Smith has indirect ties to the Bills through former Bears defensive assistant coach Gill Byrd, who is the father of Buffalo safety Jairus Byrd.
Smith is a defensive-minded coach, who would have an opportunity to put his stamp on Buffalo's revamped but under-achieving defense, which struggled last year.
The unit was among the NFL's worst despite the addition of defensive end Mario Williams, who signed a six-year, $100 million contract in free agency in March.
Marrone has been credited for turning around the Orange in four seasons. Syracuse rolled to an 8-5 finish by winning six of its last seven games this season, including a 38-14 win over West Virginia in the Pinstripe Bowl last weekend.
McCoy has become a hot prospect in his fourth season with the Broncos. He's played a key role in helping speed Peyton Manning's transition after the star quarterback signed with the team in free agency last offseason. McCoy has 13 years of NFL experience as an assistant, and previously spent eight seasons working under Broncos coach John Fox in Carolina.
Over his career, McCoy had quarterbacks reach 3,000 yards passing seven times. That includes Manning, who finished sixth in the NFL this season with 4,659 yards.
As the AFC's top seed, the Broncos are off until opening the playoffs on Jan. 12. They've allotted time for interested teams to interview McCoy in Denver this weekend. McCoy has also been linked as a candidate for coaching vacancies in Arizona and Chicago.