James B. Howell (July 4, 1816 - June 17, 1880) was a United States Senator from Iowa. Born near Morristown, New Jersey, he moved with his parents to Newark, Ohio in 1819, and attended the public schools. He graduated from Miami University (in Oxford, Ohio) in 1839, studied law, and was admitted to the bar in 1839, commencing practice in Newark. He moved to Keosauqua, Iowa in 1841, where he practiced law; he also owned a newspaper in Keosaugua and, in 1849, moved the newspaper to Keokuk, Iowa. He was postmaster of Keokuk from 1861 to 1866 and was a frequent, unsuccessful Republican candidate for state and national office.
Howell was elected as a Republican to the U.S. Senate to fill the vacancy caused by the resignation of James W. Grimes and served from January 18, 1870, to March 3, 1871; he was not a candidate for reelection to the Senate. He was one of three commissioners of the court of Southern claims appointed by President Ulysses Grant in 1871 to adjust claims for stores and supplies and served until 1880; he died that year in Keokuk, and his interment was in Oakland Cemetery.
James Howell's father, Elias Howell, was a U.S. Representative from Ohio.