Simple Summary: Preventing animal cruelty and neglect is the goal of animal protection. But it is hard to effectively address a problem without a good understanding of its prevalence and nature. While 55,000-60,000 reports of mistreatment are made to the Royal Society for the Prevention of Cruelty to Animals (RSPCA) in Australia each year, we do not know how well these data reflect what is actually happening in the community. After all, these data are reliant on people reporting what they see and therefore, probably only represent a fraction of what is actually occurring. To better understand this problem, we conducted the first extensive community survey to find out what people had seen in their communities and what they did about it. We found that animal mistreatment was (1) common, with 25.7% of people surveyed witnessing mistreatment, (2) mostly neglect with perceived underweight animals being the most common issue and (3) underreported to authorities with only 9% of witnesses reporting to RSPCA Victoria. While sobering, these findings are the first step to developing and resourcing well-informed strategies to prevent the mistreatment of animals.Abstract: While animal mistreatment is common worldwide, its true scale is largely unknown. Currently, organisations rely on community reporting (case data) and trends found therein to inform prevention activities. To investigate the prevalence, types, and responses to animal mistreatment in Victoria, we conducted a representative telephone survey (n = 1801) across six Local Government Areas (LGAs); three with high numbers of RSPCA reported cases and three demographically similar areas with low numbers of such cases. Overall, 25.7% of people surveyed had witnessed at least one incident of mistreatment in the last 12 months, with those relating to neglect or poor management predominating. No differences in prevalence were found between LGAs when socio-economic index and local government comparator group were controlled for. However, participants in regional cities recalled witnessing more separate incidents than those in metropolitan or interface areas. Actions taken after witnessing mistreatment were varied, yet many participants did nothing (27%) and only 9% reported to RSPCA Victoria. Attitudes to reporting were positive but did not predict reporting behaviour. Together, these results demonstrate that case data are not reliable indicators of the true prevalence of animal mistreatment; it is common and grossly underreported, highlighting the need for effective, evidence-based prevention programs.