Since 1856 how many democrats have been elected president?

Five members of the pre-Civil-War Democratic Party were elected U. S. President in six elections (President Jackson was elected twice).

Nine members of the post-Civil-War Democratic Party were elected U. S. President in 16 elections to date (including the forecasted winner of the 2012 election).

The pre- and post-Civil-War Democratic Parties were, for all intents and purposes, two different political parties.