Wildhaus-Alt St. Johann is a municipality in the Wahlkreis (constituency) of Toggenburg in the canton of St. Gallen in Switzerland. It was formed on 1 January 2010, through the merger of Alt St. Johann and Wildhaus (which includes also Unterwasser).
The former municipalities that would become Wildhaus-Alt St. Johann had a combined population of (as of ).
The historical population is given in the following table:
Wildhaus has an average of 157 days of rain or snow per year and on average receives of precipitation. The wettest month is August, during which time Wildhaus receives an average of of rain or snow. During this month, there is precipitation for an average of 14.7 days. The month with the most days of precipitation is June, with an average of 15.8, but with only of rain or snow. The driest month of the year is October, with an average of of precipitation over 14.7 days.
The Paleolithic cave, Wildenmannlisloch in Alt St. Johann and the birthplace of the Reformer Huldrych Zwingli at Lisighus 167 in Wildhaus are listed as Swiss heritage sites of national significance.
A PostAuto bus line links Alt St. Johann, Unterwasser and Wildhaus to , and railway stations. There is a gondola lift/chair lift from Alt St. Johann to Alp Sellamatt. From Unterwasser, there is a funicular (Iltiosbahn) and aerial tram to Chäserrugg, one of the peaks of the Churfirsten. From Wildhaus, there are a gondola lift to Gamplüt (below Wildhauser Schafberg) and chair lifts to Oberdorf and Gamserrugg.