At the same time, he studied law, was admitted to the bar in 1858, and set up his legal practice in Grinnell.
The Fourth District was then a diamond-shaped configuration of twelve counties that included Newton and Iowa City, and ran from the Missouri border to the southern edge of Waterloo.
On June 14, 1866, he was assaulted by fellow congressman Lovell Rousseau for insulting him and his home state of Kentucky during a House debate.
Grinnell lost the Republican nomination for a third term, losing by thirteen votes to Judge William Loughridge in June 1866.
Articles on his life, abolitionist activities and his obituary are available from Drake Community Library in Grinnell, Iowa.