Company vs Company's vs Companies vs Companies'

As simple as it might sound - the use of Company's, Companies and Companies' are generally mistaken by many people in writing due to sheer ignorance of the minor difference between them.


Where to use - COMPANY?

The "Company" is a (singular) collective noun, which means 1(one) company.

Even though a company represents a group of people, in the eye of law it is considered to be a single legal entity (an artificial person).

Example - Apple Inc. is an American multinational technology company headquartered in Cupertino, California.


Where to use - COMPANIES?

The plural (collective) noun of 'Company' is "Companies", which means two or more number of companies.

Example - The Standard & Poor's 500 (S&P 500) is an American stock market index based on the market capitalization of 500 large companies having common stock listed on the NYSE or NASDAQ.


Where to use - COMPANY's?

Company's - a singular possessive noun.

It means something belongs to a Company viz. assets, employees, etc.

Example - The Company's workers went on a strike in pursuit of a pay increase earlier this month.


Where to use - COMPANIES'?

Companies' - a plural possessive noun.

It means something common belongs to a number of Companies.

Example - Record Companies’ U.S. Revenue Up 8.1% in First Half of 2016.


COMPANIES'S

The use of Companies's is incorrect in written English.

Although you may still find the use of apostrophe + s after plural nouns at may places on the net and books, still this use is considered wrong widely by many authors, writers and people with sound knowledge in English grammar.