The statistic comes from the European Central Bank's study on Cash Use by Household in the Euro Area, published in November 2017.
The report presents estimations of the number and value of cash transactions in all 19 euro area countries in 2016, based on survey result as well as figures on main payments by demographic. In terms of number, the use of cash by households in Portugal was 81%.
"Comparing the use of cash per country, it can be concluded that cash was used most in southern euro area countries, as well as in Germany, 19 Austria and Slovenia (resulting in country shares of 80% or above for all POS transactions; see Chart 2). The market share of cash was lower in Latvia, Lithuania, Slovakia and Ireland, ranging from 71% to 79%. Belgium, Luxembourg and France follow with a cash share ranging between 63% and 68%. The Netherlands, Estonia and Finland had the lowest shares, ranging between 45% and 54% of all payments at POS. 20." (p/ 19)
"In 12 countries, a majority of respondents said that they never pay a fee when withdrawing cash; however this varied from 53% in Italy to 81% in Malta. In Slovenia and Slovakia, less than one-third of respondents responded that they never have to pay a fee." (p.48)
"Furthermore, in addition to Cyprus, in Austria, Malta, Ireland, Greece and Spain a larger share of respondents stated that they prefer using cash over cashless means of payment." (p. 52)
“In 2016 euro area consumers carried on average €65 in their wallet. Germans carried on average the most (€103) in their pockets, followed by the Luxembourgers (€ 102) and the Austrians (€89) (see Chart 20). On the other hand, the Portuguese carried, on average, the least (€29), followed by the French (€32) and the Latvians (€41).” (p. 34)