There are two species of gray treefrogs in Maryland: Gray Treefrog (Hyla versicolor) and Cope’s Gray Treefrog (Hyla chrysoscelis). You can’t tell them apart by looking at them. They do however have different calls.
This frog is a Cope’s Gray Treefrog (Hyla chrysoscelis) found on my deck. I’ve heard its call and the map (link below) confirms its range in Southern MD.
Cope’s Gray Treefrog