Which are the three top agencies that deal in credit ratings?

1. The Big Three credit rating agencies are Standard & Poor's (S&P),Moody's, and Fitch Group. S&P and Moody's are based in the US, while Fitch is dual-headquartered in New York City and London, and is controlled by the France-based FIMALAC.

In which country?

Yes, they are

Moody’s Investors Service, standard poors and fitch 

Standard & poor's, Moody's and Fitch group