Irregular plural nouns break the rules when it comes to using apostrophes.
For regular plural nouns, the apostrophe goes after the -s. An example would be:
I don’t like that dining room set because the chairs’ legs are iron.
But irregular plurals will rarely have an -s to indicate more than one, such as in the word people, children, men, and women. In this case, since there is no -s on the word, add the apostrophe as you would on a singular verb, but keep in mind that they are still plural.
The People’s Court (the court belongs to all the people)
The Children’s Room (the room belongs to more than one child)
The Men’s Section (the section has clothes for men)
The Women’s Department (the department has items for women)
Sometimes you will see Ladies’ Department. That is correct, too. The word lady is not irregular.