After a year, he moved south to Grant County, settling in the town of Platteville, which remained his home for the rest of his life.[2][3] At the second session of the 4th Wisconsin Territorial Assembly, Eastman was selected to serve as secretary of the Territorial Council (the upper legislative chamber), and was retained for the third and fourth sessions. He resigned about mid-way through the 4th session, on January 19, 1846. In 1847, he was a Democratic nominee for county commissioner, but the Whig Party carried nearly every office in Grant County that year. In 1848, Eastman commissioned a survey and plat on a section of land he owned in the town of Wingville, establishing the settlement of Montfort.[3]
The first session of the Wisconsin circuit court in Grant County was held in October 1848, and Eastman was among ten lawyers admitted to practice before that court. In 1849, he was elected chairman of the Platteville town board, which made him ex officio a member of the county Board of Supervisors.[3]
In 1850, Eastman ran for Congress on the Democratic ticket in what was then Wisconsin's 2nd congressional district. The 2nd district then comprised the entire western half of the state of Wisconsin. He defeated the incumbent Whig Party congressman, Orsamus Cole, and went on to serve in the 32nd Congress. He was re-elected in 1852, but declined to run for a third term in 1854. He returned to Platteville and resumed the practice of law.
Ben Eastman was one of twelve children born to Samuel Eastman and his wife Jane (née Hitchcock). Samuel Eastman was a successful merchant in Maine and a state senator. The Eastman family were descended from Roger Eastman, who was born in Wales and emigrated to the Massachusetts Bay Colony in 1638 aboard a ship named the Confidence.[6]
Several of Ben's brothers also ultimately settled in Wisconsin and made careers there.
Ben's eldest brother, William Henry Eastman, (born 1808) settled in Green Bay in the 1870s after a career in the east.[7]
George W. Eastman (born 1824) followed Ben to Wisconsin and settled in Platteville with him in 1850. He was a physician and banker and served as a surgeon and medical inspector for the Union Army.[8]
Ben Eastman married Charlotte Sophia Sewall of Hallowell, Maine, in 1841. They had no children.[2]