Jefferson is a city in Greene County, Iowa, United States, along the North Raccoon River. The population was 4,626 at the 2000 census. It is the county seat of Greene County. It is the home of the Mahanay Memorial Bell Tower, 168 feet (51 m) tall, located on the town square, and visible for miles. The tower is named for Floyd Mahanay, a philanthropist and former resident. Jefferson is bisected east to west by the old Lincoln Highway (formerly U.S. 30). A new U.S. 30 is located about one mile to the north.
While platted and settled a few years earlier, "New Jefferson" was organized in the winter of 1855-56 and officially incorporated in January 1872. It began as a farming community and remains so today. The first settlers of the new city were the family of George S. Walton who built there in 1855. During the Civil War, Jefferson as well as Greene County contributed its sons to raising Company H, 10th Iowa Infantry (1861) and Company E, 39th Iowa Infantry (1862). The railway came to Jefferson in the decades after the Civil War. Jefferson's first mayor was Mahlon Head, elected in 1872. Jefferson's library was completed in 1904 through the generosity of the Carnegie library fund. The stretch of Lincoln Highway that runs through Jefferson was completed circa 1924.
Jefferson is located at 42°1′0″N 94°22′36″W / 42.016667°N 94.37667°W / 42.016667; -94.37667 (42.016749, -94.376753).