For what it's worth, all indications are that Maryland was going to secede in late 1861 but a number of state legislators got arrested (much like the other Upper South states which seceded after events eventuated).
Maryland, like all the other Border States, flatly rejected secession in
early 1861. (Which is also when the Upper South states declared secession.) The legislature voted unanimously that it lacked power to declare secession, and 53-13 against calling a convention that would have such power. This was in April, and the legislature met in Frederick, with no Union soldiers present or even within 20 miles.
In
late 1861, several members of the legislature (one senator, eight representatives) were arrested for pro-Confederate activities, such as recruiting for the CS Army. Some Neo-Confederates conflate this event with the events of April, claiming that the arrests were made to coerce the legislature at that time. There is no substantial evidence that formal secession was ever supported by a majority in Maryland.