The disclosed computer-implemented method for identifying message payload bit fields in electronic communications may include (i) monitoring messages transmitted via a network, (ii) selecting a plurality of messages transmitted via the network, each of the plurality of messages comprising an identical message identifier corresponding to a specified message type having a payload, (iii) determining for each bit position in the payload of the specified message type, a quasi-entropy value based on a proportion of occurrences of a first bit value and a proportion of occurrences of a second bit value at each corresponding bit position in the plurality of messages, and (iv) identifying at least one of a near-random bit field, a periodic bit field, and a constant bit field within the specified message type based on the determined quasi-entropy values. Various other methods, systems, and computer-readable media are also disclosed.