Neuendorf has an area, as of 2009, of 7.16 square kilometers (2.76 sq mi). Of this area, 3.51 km2 (1.36 sq mi) or 49.0% is used for agricultural purposes, while 2.37 km2 (0.92 sq mi) or 33.1% is forested. Of the rest of the land, 1.24 km2 (0.48 sq mi) or 17.3% is settled (buildings or roads), 0.01 km2 (2.5 acres) or 0.1% is either rivers or lakes.
Of the built up area, industrial buildings made up 4.3% of the total area while housing and buildings made up 6.0% and transportation infrastructure made up 4.6%. Power and water infrastructure as well as other special developed areas made up 1.4% of the area Out of the forested land, all of the forested land area is covered with heavy forests. Of the agricultural land, 41.3% is used for growing crops and 5.2% is pastures, while 2.5% is used for orchards or vine crops. All the water in the municipality is flowing water.
The municipality is located in the Gäu district, near the Dünnern river. It consists of the linear village of Neuendorf.