The 23-year-old Sakho, already a France international, arrives from Ligue 1 champions Paris St Germain while 20-year-old Ilori joins from Sporting Lisbon.
Sakho told the club's official website: "I'm delighted to be here. I'd like to thank everyone for the welcome.
"I came here because the project that is in place at Liverpool interests me. I'm really looking forward to playing my first game.
"I know the Liverpool fans are fantastic and while I was in France, it was clear for me to see they are amongst the best in England."
Ilori added: "It feels great being a Liverpool player - coming to the Premier League has always been a dream for me.
"I'm going to try and achieve everything I can. I want to play as much as possible and we'll see what the future holds. I will give my all and try my best to help the team.
"I know the history of the club and the Premier League is the best league in the world, in my opinion," added Ilori. "Liverpool have a great team and I think it's the place for me to be at the moment.
"I know there have been some great teams here in the past and the club has won a lot of trophies and I want to be a part of it."
In addition, Chelsea winger Victor Moses became Liverpool's eighth summer arrival before lunchtime on Monday as he signed a season-long loan deal.
Brendan Rodgers' side moved to the top of the Premier League table by beating rivals Manchester United 1-0 on Sunday.