This 2014 research report from a company called Life Cycle Associates contains a nice table and graph showing
the volume weighted carbon intensities (g CO2 e/MJ) of U.S. petroleum
gasoline and corn ethanol over time based on the historical crude oil and ethanol plant resource mixes and future projections.
From: Boland. S. and Unnasch. S. (2014) Carbon Intensity of Marginal
Petroleum and Corn Ethanol Fuels. Life Cycle Associates Report LCA.6075.83.2014, Prepared for Renewable Fuels Association. (link to PDF)
The researchers also say that
The CI for corn ethanol reflects the most recent estimates of land use conversion from the University of Illinois and Argonne National Laboratory.
However, there is no reference to these estimates, so I'm not sure from which year they are. Based on the table I suspect the most recent used data is from 2012.
I also found one other source, which is this webpage of the U.S. Energy Information Administration, published in March 2011. Their data is based on this document of the California Air Resources Board and on research done by Purdue University and Argonne National Laboratory
Graph from: https://www.eia.gov/todayinenergy/detail.cfm?id=750