I would pass on mulberry trees -- birds eat the fruit and then you have purple stains everywhere as the birds poop on you car, house, driveway, ....

Pussywillows grow fast but I don't know how 'neatly' trimmed you want to keep your hedge.

You might want to consider something evergreen so you can have privacy in the seasons other than summer. 6' tall Arborvitea is available in stores around here during planting season.
Sunflowers need to be planted each spring, so until the middle of summer, you'd have no privacy. Then in September the squirrels topple the plants to get at the seeds.
I agree w/ Paul - Mulberry trees are a nuisance.

forget about mulberry or any fruiting trees unless you make it an orchard- those things have tendency to fall off and clatter your yard. Privet is excellent, tough divider and smells nicely in the spring. Nothing special though, but will grow with no care.

You mention wanting something to overtake 12'...so unless you want to wait for your grandkids to do the clipping---privet will take some time to get up to the height...and if you just leave it to gain that height, it will be so out-of-shape, you will want to get rid of it.

White Cedar...as you call it "arborvitae"...is the one to please you.
Mind you, it has to be clipped....but planted at the 3, 4 or 5 foot height, then cut back about 6", will grow --once established, a foot a year.
12' you want.....12' you'll get in a short time--but be warned..12' is not where it'll stop...15', 20'...
but can be kept lower by annual clipping.

Seconding Arborvitae for your area (I'm in northern Illinois, about an hour from you).

Proper name:
northern white-cedar --- Cupressaceae Thuja occidentalis L
Cultivars:
'Aurea' - A golden globe that needs little shearing.
'Boisbraind' - A plant 10 feet tall with dark green,
burn resistant foliage.
'Brabant' - This cultivar tends to form one central
leader thus minimizing stem damage from winter snows.
'Brandon' - A fast-growing, cone-shaped plant about 15
feet tall and 4 feet wide. Reported as suitable for
use on harsh sites.
'Chalet' - A narrow plant with a rounded top and lime-
green foliage. It will be 10 to 15 feet tall.
'Compact American' - A compact, pyramidal form reaching
a height of 25 feet and a spread of 8 feet.
'Danica' - A slow-growing, compact globe with dark
green foliage.
'Degroot's Spire' - A narrow, columnar form.
'Douglasii Pyramidalis' - A dense, columnar form with
twisted dark green foliage.
'Elegantissima' - A slow-growing, dense plant with
yellow branch tips.
'Filiformis' - A pendulous plant with long, thread-like
branchlets and bright green new growth.
'George Peabody' - A broad, upright plant with yellow
foliage. The foliage becomes more orange in winter.
'Gold Cargo' - A cultivar with gold foliage that is
reported to resist winterburn. The plant can be 25
feet tall and 6 feet wide.
'Golden' - A broad, upright form with bright yellow new
growth.
'Golden Globe' - A uniform oval with foliage a soft
yellow.
'Hetz Midget' - A slow-growing, compact plant.
'Hetz Wintergreen' - A narrow, upright form reaching a
height of 60 feet.
'Holmstrup' - Dark green foliage that holds its color
in winter. Broadly pyramidal.
'Little Gem' - A globe-shaped plant reaching a height
of about 3 feet.
'Little Giant' - A slow-growing, globe-shaped plant
with bright green foliage all year.
'Masonic' - Pyramidal form about 25 feet tall and 5
feet wide.
'Niagara Compact' - A globe-shaped plant more compact
than 'Woodwardii'.
'Nigra' - A symmetrical form with good dark green
foliage color.
'Pendula' - An open, weeping form with dark green
foliage.
'Pygmy Globe' - A dwarf, globe-shaped plant with bright
green foliage. Needs little shearing.
'Pyramidalis' - A narrow, columnar plant often used for
screens.
'Rheingold' - Yellow foliage that becomes orange yellow
in winter.
'Sherman' - A pyramidal form reaching a height of 30
feet and a spread of 12 feet.
'Sherwood Moss' - A dwarf plant 4 to 6 feet tall.
'Smaragd' ('Emerald') - Narrow habit with glossy green
summer color. Reported as resistant to spider mites.
Plants will be about 15 feet tall and 4 feet wide.
'Sudworthii' - Upright, broad plant with yellow
foliage.
'Sunkist' - A compact, broad plant with orange-yellow
foliage.
'Techny' ('Mission') - A fast-growing plant with dark
green foliage. Usually about 15 feet tall.
'Tiny Tim' - A compact, upright mounding plant.
'Umbraculifera' - A rounded, irregular plant, nearly 3
feet tall and 5 feet wide.
'Unicorn' - A narrowly compact plant with dark green
foliage.
'Wareana' - A slow-growing, broadly upright plant.
'Wintergreen' - A pyramidal form reaching a height of
30 feet that retains good green color in winter.
'Woodwardii' - A rounded form that retains its shape
without shearing.
'Yellow Ribbon' - A narrow, upright habit is combined
with yellow foliage all year.

I'm always sorry to see homeowners want 'fast' trees. They just dont measure up in the long run. Either they sucumb to disease, or they drop twigs and limbs all year, or crack in high winds.

Better to spend money on one or two larger trees, such as arborvitae (above), and intersperse with deciduous natives
like hornbeam, serviceberry or other smaller trees.
It depends on how much length you need to cover.
Personally, I dont care for any of the 'yellow' evergreens unless mixed with the deep green or blues. Alone, the yellows look like they are diseased.

The mix of evergreen (for shelter/nests) and hornbeam or serviceberry (for food) will attract song birds to your yard.
Pondy

Could you use Laurel Leave Hedging in Illinois?

Honeysuckle but make sure to protect in the winter from strong winds

English Laurel makes for a beautiful hedge, but... to remain beautiful it needs shaping at least 2-3 times a year. If allowed, it will grow 30-40 ft in the air, (good idea if you truly want privacy and no view of the neighbors or their structures -- in which case just trim the sides...) However, keeping the top well trimmed and squared-off is what gives it class. A 6-8 ft. well pruned Laurel hedge is very elegant and allows reasonable privacy, (corners can be rounded or squared off)