Flawil has a population (as of ) of . , about 26.5% of the population was made up of foreign nationals. Of the foreign population, (), 138 are from Germany, 516 are from Italy, 964 are from ex-Yugoslavia, 64 are from Austria, 138 are from Turkey, and 516 are from another country. Over the last 10 years the population has grown at a rate of 4.2%. Most of the population () speaks German (84.5%), with Italian being second most common ( 3.4%) and Serbo-Croatian being third ( 3.4%). Of the Swiss national languages (), 7,872 speak German, 27 people speak French, 313 people speak Italian, and 10 people speak Romansh.