Is the word suburb usually used in plural or singular?

My dictionary suggests following examples:
• The suburb of London
• London suburb
• They live in the suburbs

Why is this word used in its plural form in the last sentence?
Can I say, for instance, they live in the suburb? Or: They live in the suburb of London?

Question

Is the word suburb usually used in plural or singular?

My dictionary suggests following examples:
• The suburb of London
• London suburb
• They live in the suburbs

Why is this word used in its plural form in the last sentence?
Can I say, for instance, they live in the suburb? Or: They live in the suburb of London?

Answer

Not really sure why but you can say:
They live in a London suburb
They live in a suburb of London
They live in a suburb
They live in the suburbs

Answer

It can be either.        In general usage:

He lives in the suburbs.   OR He lives in a suburb.

Specific examples:

Edina is a suburb of Minneapolis.         
Edina, Bloomington, and Maple Grove are suburbs of Minneapolis.

Answer

Well, I would say, Suburb is singular and Suburbs is the plural version, but either can be used, depending on the context.
In the examples you used, wither is fine.