A method of operating a memory controller includes: collecting hard decision information based on data read from memory cells of a monitoring unit using a normal read level; collecting soft decision information based on data read from the monitoring unit using one or more offset read levels that are different from the normal read level; storing first strong error information determined based on the hard decision information and the soft decision information in a memory in the memory controller; and updating second strong error information determined for the monitoring unit in the memory after the first strong error information is stored. The second strong error information is used to correct an error in data read in response to a read request from a host.