Isaac Mosher Preston (April 25, 1813 – March 6, 1880) was an American politician.
Preston was born in either Cambridge, New York, or Bennington, Vermont in 1813, the son of a veteran of the American Revolutionary War.
He subsequently relocated to Marion, Iowa, in November 1842, and served as district attorney between December 1845 and March 1847, until his appointment as United States District Attorney for Iowa by President James K. Polk.
Preston had previously been elected probate judge for Linn County twice, in 1843 and 1846.
Preston moved to Cedar Rapids, Iowa, approximately one year before his death at age 66 in 1880.