Alt St. Johann has a population () of 1466. , about 9.4% of the population was made up of foreign nationals. Of the foreign population, (), 19 are from Germany, 3 are from Italy, 91 are from ex-Yugoslavia, 8 are from Austria, and 37 are from another country.
Most of the population () speaks German (93.0%), with Serbo-Croatian being second most common ( 3.3%) and Albanian being third ( 1.4%). Of the Swiss national languages (), 1,351 speak German, 3 people speak French, and 3 people speak Italian.