The aim of this study was to develop a decision support tool for nurses to facilitate aging in place of people with dementia and to test its usability. Nurses play an important role in detecting practical problems preventing persons with dementia (PwD) from aging in place and advising them on possible solutions. These are complex and challenging tasks for nurses. A mixed methods study was conducted. The content development of the App comprised a literature and internet search, and individual and group interviews with professionals (n = 8) and researchers (n = 5). The technical development was an iterative process in which usability was tested by the project team (n = 4), experts (n = 6), and end-users (n = 9), using heuristic evaluation, a think-aloud approach, and a questionnaire (PSSUQ). The App contains a structured problem assessment for three problem domains—self-reliance, safety, and informal care—based on validated questionnaires and self-formulated questions. The problem assessment is linked to an overview of possible solutions for the problems detected. Three prototypes have been developed. The users of the third prototype were overall satisfied with the App as they scored on average 1.7 on the PSSUQ (range 1–7 and lower scores indicating higher satisfaction). A user-friendly prototype of the decision support App is now available. Users indicated to be very willing to use to App in daily practice. However, besides further technical development, implementation of the App into practice requires evidence supporting its efficacy, feasibility and effectiveness.