The area was already inhabited in the Upper Paleolithic, according to archaeological findings (the oldest ones in Zala county.) Later the area has been inhabited by Celts.
The first written mentions of the town are as Egerscug (1247) and Egerszeg (1293); the name means "alder-tree corner" and is probably a reference to the town's situation in the angle where two rivers meet. King Béla IV donated the town to the diocese of Veszprém in 1266, so that it became church property. As Egerszeg lay somewhat distant from Veszprém, however, the taxes paid by the town often ended up in the pockets of such local oligarchs as the Kőszegi family.
In the 14th century Egerszeg was the largest town of the area. Between 1368 and 1389 it was a royal town for a short time, then Sigismund I donated it to the Kanizsai family who traded it for another town with the bishop of Veszprém. Zalaegerszeg remained their property until 1848.
In 1381 the town built a stone church. In 1421 Egerszeg was granted oppidum status, which meant they could pay taxes once a year and the citizens could elect their own judge. The population grew quickly, and by the 16th century Egerszeg became the de facto centre of Zala comitatus.
In the 1530s development was brought to a halt. Taking advantage of the power of the king being weakened, the owners of the surrounding lands attacked the town often, and the Ottomans already began to occupy Hungary after the Battle of Mohács in 1526. From 1568 the town was fortified, a castle was built. The Ottomans attacked the town for the first time in the late 1570s, but they failed to capture it.
After Kanizsa fell to the Ottomans, the strategic importance of Egerszeg grew, but the castle was severely damaged in 1616 and captured by the Ottomans for a short time in 1664. The citizens suffered not only from the war, but from plagues and heavy taxes as well.
Egerszeg, even though it was on the periphery of the comitatus, became its
