The economic development of Biecz resulted in a population boom. A census conducted by the judiciary from 1388 to 1398 lists the names of 515 heads of households. Taking into account that contemporary families consisted on average of six people, it is believed that Biecz and its suburbs had at least 3,000 residents. By the mid-16th century, Biecz had a population of 3,700, the highest population the city achieved during the Middle Ages. Starting in the 17th century, Biecz went into a decline, its population slipping to approximately 1800 people in the first half of the 17th century, and then to 462 inhabitants in 1662.