Seengen is a municipality in the district of Lenzburg in the canton of Aargau in Switzerland.
Seengen lies in the Seetal valley to the north of Lake Hallwil.
The municipality has an area, as of 2009, of 9.69 square kilometers (3.74 sq mi). Of this area, 4.97 km2 (1.92 sq mi) or 51.3% is used for agricultural purposes, while 3.13 km2 (1.21 sq mi) or 32.3% is forested. Of the rest of the land, 1.33 km2 (0.51 sq mi) or 13.7% is settled (buildings or roads), 0.01 km2 (2.5 acres) or 0.1% is either rivers or lakes and 0.18 km2 (0.069 sq mi) or 1.9% is unproductive land.
Of the built up area, housing and buildings made up 9.3% and transportation infrastructure made up 2.6%. Out of the forested land, all of the forested land area is covered with heavy forests. Of the agricultural land, 35.6% is used for growing crops and 11.4% is pastures, while 4.3% is used for orchards or vine crops. All the water in the municipality is in rivers and streams. Of the unproductive areas, 1.7% is unproductive vegetation.