Lapado, who will turn 25 tomorrow, has signed a temporary six-month deal at Roots Hall, with the option of a further year on top of that.
The striker has made just two senior appearances for Palace since joining the Eagles in March 2016, but did feature in a Premier League match against Manchester United in September.
Ladapo began his youth career with Southend before joining Colchester United in 2010.
"I was at Oldham for the first part of last season and then Shrewsbury in the second half and I enjoyed my time with both clubs, but now I'm back at a club where I started off as a kid and I want to do really well and make my mark," he told the club's official website.
"I'm hoping to get into the team on Saturday because it's a huge game and I just want to hit the ground running; if I'm involved in the game this weekend then I hope it's a good debut for me."
Ladapo, who will wear the number 19 shirt at Roots Hall, could make his debut against Peterborough United this weekend.