The mandatory American Community Survey (ACS) takes 40 minutes to complete on average and is often answered using a mail-out/mail-back form or the ACS online instrument on a desktop or laptop. However, recent analysis has indicated that there is a small but growing segment of respondents who answer the ACS using their mobile devices (Horwitz, 2015). In Phase I of this research, the Center for Survey Measurement (CSM) conducted a usability test of the ACS on smartphones and tablets, prior to the screens being formatted in a mobile-friendly design. Users experienced many usability challenges that could lead to increased errors and frustrations (see Olmsted-Hawala et al., 2016). Consequently, the ACS team decided to update the online screens to allow for a mobile-friendly design. In Phase II, members of CSM and the Decennial Statistical Studies Division (DSSD) collaborated to investigate how respondents interact with the ACS online instrument with a smartphone or tablet when the screens had been designed for a mobile-friendly experience. The goal of the evaluation was to identify how the online ACS performed for respondents who answered while using their own mobile device (e.g., smartphone or tablet) on the newly updated screens as well as to compare user performance from Phase I with Phase II. Finally, the study aimed to identify screens which continued to be more challenging for respondents to work on with a mobile device. Usability findings indicate that, in general, users are more satisfied with the mobile-friendly design than they were with the mobile un-optimized design. However, while the instrument is now in a mobile-friendly design, there are a few areas where modifications to the design could be made to improve the user experience. These design modifications are detailed in the results section.