The 33-year-old singer, who has two kids -- daughter Maxwell and son Ace Knute with Johnson -- is planning to have only close friends and family members for the nuptials, reported Contactmusic.
"There will probably only be 75 to 100 guests. Jessica will definitely not invite more if she can help it. She wants to have only really close family and friends - the kind of people she speaks to a regular basis," a source said.
The wedding was initially supposed to take place in 2012 over the Christmas holiday at Hawaii but got postponed after Simpson got pregnant again.