It appears that Catlin was an active commander of small force units in SE MO throughout 1861 and 1862. He was with Prentiss and then Grant ending up at Belmont. Served as Adjutant for a bit and then Aide de camp to General Grierson being killed in Mississippi in 1864. Court records in Jacksonville list his date of death as Feb 22, 1864. (http://morgan.illinoisgenweb.org/probate/pro_002.htm) Note his father Joel is listed as administrator.

Greirson knew him prior to the war and listed his hometown as Jacksonville IL.

See "A Just and Righteous Cause: Benjamin H. Grierson's Civil War Memoir"
http://books.google.com/books?id=3q3H7jFVyTEC&dq=lt+james+k+catlin&source=gbs_navlinks_s

His Civil War career started with Delano's Adams County Volunteer Cavalry under Fremont then Prentiss before enrolling in the IL 2nd Cav.

See Bio on his brother here for family history: http://morgan.illinoisgenweb.org/1906/c_001.htm

FWIW.

John R