One man “pleaded guilty to DWI.” Another “pled guilty of DWI.” A third “entered a plea of guilty to DWI charges.”
What’s going on, aside from way too much drinking?
Prepositions are little words with great power. As discussed here many times, just a few letters can radically alter meaning. Just change “I’m stuck on you” to “I’m stuck with you,” and suddenly you’re alone.
A preposition creates a relationship between two parts of a sentence. Or, as Wikipedia so elegantly* puts it, “Prepositions (or more generally adpositions, see below) are a grammatically distinct class of words whose most central members characteristically express spatial or temporal relations (such as the English words in, under, toward, before) or serve to mark various syntactic functions and semantic roles (such as the English words of, for).” (Just that is enough reason to avoid Wikipedia as a first point of reference.)
Many prepositional phrases are idiomatic, meaning they don’t necessarily reflect what the actual words mean, or the rules of grammar. (“Back away” makes perfect literal sense, for example; “back down” less so, though the idiom is clear.)
And so it is in prepositional phrases involving pleas of guilty. Note that you would never say “pleas to guilty,” or “pleas for guilty.” But some phrases get more leniency.
“Of” has among its many definitions a sense of possession (a bottle of wine) or result (die of boredom). For its part, “to” also has a result meaning (sentenced to prison), as well as directional (go to work). Any of those definitions play well with “guilty (your preposition here) DWI” or “guilty (your preposition here) DWI charges.”
But there can be a subtle difference.
Years ago, style at The Des Moines Register, and possibly elsewhere, was to say that someone pleaded guilty of an act, but pleaded guilty to the accusation. In other words, someone would plead “guilty of DWI,” but would plead “guilty to DWI charges.” Some logic is at work here: It makes no sense, even idiomatically, for someone to plead “guilty of charges.” So when the crime (DWI) became a modifier instead of a noun (or gerund), the preposition had to change accordingly.
Outside of the justice system, most idioms involving “guilty” use “of” (“we’re all guilty of using idioms”), but those idioms rarely involve modifiers.
Few style guides address this question. The Associated Press Stylebook seems to favor the act vs. accusation usage, with one entry saying “pleaded not guilty to four counts of first-degree murder” (accusation) and another saying “guilty of funding terrorism” (act). But it also has an entry that says “pleaded guilty in 1957 to criminal contempt,” using “to” for an act rather than an accusation.
You can make your own choice, based on how precise (or nit-picky) you want to be. Just try not to be guilty of inconsistency.
As for “pleaded” vs. “pled,” while they are generally interchangeable as the past tense of “plead,” “pled” is considered more colloquial, and weak. Most style guides prefer “pleaded.” And “entered a plea of guilty”? Convicted of verbosity.