The Township of Hillsborough et al. v. Cromwell case in 1945 revolved around a dispute over property taxes. The plaintiff, Cromwell, owned land within the township and argued that his property was assessed at a higher rate than other similar properties in violation of the Fourteenth Amendment's Equal Protection Clause. He sought to recover excess taxes paid under protest for three years prior to filing suit. The Supreme Court ruled against Cromwell, stating that he failed to prove intentional discriminatory taxation by local authorities or systematic undervaluation of other comparable properties. The court also noted that minor discrepancies in tax assessments are inevitable due to the complex nature of real estate valuation and do not necessarily constitute unconstitutional discrimination. Furthermore, it was highlighted that taxpayers should first exhaust state remedies before seeking federal relief unless there is clear evidence showing futility in pursuing such avenues - which wasn't demonstrated by Cromwell. This ruling reinforced two key principles: firstly, proving unequal taxation requires demonstrating intentional discrimination; secondly, taxpayers must generally pursue all available state-level remedies before turning to federal courts for relief.

In the dissenting opinion for Township of Hillsborough et al. v. Cromwell, Justice Robert H. Jackson argued that the majority's decision to allow a taxpayer to challenge an assessment without proving actual damage was a departure from established legal principles and could lead to unnecessary litigation. He contended that taxpayers should not be able to contest assessments unless they can demonstrate concrete harm or unfair treatment, as this would prevent frivolous lawsuits and ensure efficient use of court resources. Furthermore, he expressed concern about potential abuse of this new right by wealthy individuals seeking tax reductions at the expense of other citizens who may lack resources for similar challenges.