Designing surveys for mobile data collection raises a number of programming issues for researchers. For example--should we design an app that can be downloaded by the user or a Web application that would be rendered based on type of a mobile device? What are the benefits or drawbacks using app or Web based surveys? How should we display questions to accommodate different screen sizes and formats of devices? Should the user use the keyboard to enter date or should we use date picker? Should we automatically capitalize the first letter entered for names and addresses? In preparation for the 2020 Census, the Census Bureau developed and cognitively tested several android apps for three different decennial census forms: a household level questionnaire; a group quarters questionnaire; and a questionnaire used for people who did not receive the household questionnaire. For this study, we used Android-based tablet and smartphone devices to conduct the cognitive and usability testing. The presentation will review the challenges faced by the project team, our findings from two rounds of interviews, and the design changes that we made as a result of testing. The audience will have an opportunity to use and compare the questionnaires designed for the tablet and smartphone and compare the differences themselves. We will also talk about next steps in this work and how we plan to address some of the challenges of preparing these apps for use in the field.