The campground at Grand Haven State Park is very near the water but you camp in a parking lot around sand. If you love beach camping you will like that park.
Hoffmaster State Park is located between Muskegon and Grand Haven. Muskegon State Park is located north of Muskegon. At both parks you have to walk to the beach.
Grand Haven and Hoffmaster State Parks are very popular and it may be difficult to get a good site or one at all.
Here is a link to the
Muskegon County Parks . Meinert Park is located near the beach on Lake Michigan. The campsites are not right on the beach but within walking distance as are the sites at Hoffmaster and Muskegon. You can now make reservations online for the Muskegon County Parks.
As you travel further north you may wish to check out Mears State Park near Pentwater. I also second the vote for Lake Leelanaw. We have stayed there and it is very nice. You can rent boats there, too.
Have fun! I grew up in Western Michigan and we will be there in July also, for our high school class reunion and a family reunion!