Mount Blue is an awesome Maine State Park about 2 hrs. north-west of Portland, 1hr from the White Mts. in NH and 1.5 hours from the Quebec border. 

Chock full of activities from lakefront lounging, swimming, dark sky stargazing, fishing, biking, hiking, paddling and boating all from your campsite or nearby within the park. 

Our group had the South Shelter group camping area, lakefront with small beachfront where you can have a decent sized bonfire and keep kayaks, SUPs, etc. 

View is amazing, looking out across lake to Mount Blue and Tumbledown. Took the quick but steep hike up to the fire tower at Mount Blue's summit, about 3.5 miles RT. 

Also really liked: 

new and clean showers (individual shower rooms with hot water, are free!)

trails that link all campsites to the lake

super friendly staff

log cabin shelter at lake with a huge stone fireplace - didn't use it but this would be great for a group dinner

group site was spacious and slopes up from lake with plenty of shaded tent areas - we had about 8 tents and didn't feel crowded in the least

group site also has a spacious shelter and fire pit area at the top of the slope, with 4 picnic tables - cool for the showers we experienced when several people could fit inside under the roof, play games and wait out the storms. 

Of note: 

The shower house is located a good ways off from the group sites, over in the tent and RV/trailer site area. Some of us walked ands others biked or drove over. 

At the group site there is a decent outhouse but no running water - so plan for that. 

Showers were diagonal from site 9 in the camping area. 

Def. check this beautiful state park out, and you can support Maine State Parks by purchasing an annual pass for around $105.