Source: U.S. IRS Tax Assessment List 1862-1918, Washtenaw, Michigan, USA, District 3, p133 ; line number 15, for Daniel C. Fenn, 1864. NARA M773, NARA Roll 8, database online, www.ancestry.com.
My second great grandfather, Daniel C. Fenn, is on the 1864 Tax List for Washtenaw county, on line 15; his brother, Orlo H. Fenn, is on line 4. This tax was collected during the civil war and used to help pay for the war. The National Archives has an article, "Income Tax Records in the Civil War Years" in their Prologue magazine and it is available online here.
Daniel C. Fenn was living in Sylvan Township, he had 1 Horse Carriage and was taxed $1 in Class C.
Orlo H. Fenn was living in Sylvan Township, he had income of $183 and was taxed $5.49 in Class A.
The 1864 Tax List helped me to know where my ancestors were living between the census dates of 1860 and 1870. It gave me a look into their welfare at the time, as well. It looks like Uncle Orlo was a little better off than his brother.
The highest tax paid on this page was $74 from Henry Goodyear for income of $2400 and one two horse carriage. Most of the people on the page paid less than $10.
Don't overlook these tax records as a source in your research, you can learn a lot about your ancestor in the limited information that was recorded.