This report documents two rounds of usability testing conducted on successive iterations of a prototype user interface developed for potential online data collection in the 2010 Census. Following the first round of testing, many usability recommendations and other changes were implemented. The second round of testing found the prototype user interface to be generally usable by sighted participants but unusable by those with visual disabilities. Methods of testing, results, and recommendations are detailed in this report. For reasons unrelated to usability, further development of a system for online data collection in the 2010 Census was cancelled by the Director of the Census Bureau.