From my understanding, in IPv4 addressing, the first 2 octets identify the network, meaning 2^16 networks can exist. But that doesn't seem even closly enough as the population in even USA is above 300 millon meaning there are probably more than 65,536 houses with internet accessable networks. Is there something I'm missing?
Note that classful networking has been obsolete since 1993.
In theory, you could split the whole address space into /31 subnets for point-to-point connections, so hypothetically there could be 231 networks. For great answers on how subnetting works, see this question.
Also, when NAT with private addressing is used, the number of possible networks can be much larger (behind each public IP could be a private network which could in turn use NAT internally).