USA Today provides an infographic detailing the number of corruption convictions per 100,000 people. Using statistics from the Department of Justice, the article boldly declares that North Dakota is the most corrupt state in the Union while infamous Illinois comes in at a late 17th:
Using conviction rates of corruption as a proxy for the number of corruption cases is obviously misleading. The most corrupt system would have zero convictions. While there are more reliable academic measures on corruption, I am sure this data could be better measured and understood a mixture of measures including state openness (more open public offices are likely to have either less corruption or higher conviction rates), judges or police officers per 100,000 (measure of the size of the judicial system - I imagine protection to be an economy of scale), immigration into the state (non-citizen and US-citizen - those with the least understanding of the rules may be the easiest to take advantage of), and a few other measures found in the literature.
Or one could just never take US Today graphics seriously and save some time.