There are 4,02,76,980 accounts in the mutual fund industry as at December 2014, of which 99% is accounted for by individual investors, according to AMFI data.
There were 38,621,017 retail investor accounts, 1,322,099 folios of of HNI accounts and 333,864 folios of institutional investors accounts.
Account refers to a folio. An investor may have multiple accounts in a single fund or across funds.
This is therefore not a count of number of investors, but number of accounts.