Closest boat launch to Fairview St park?

Park has a launch.

Like these guys said, the park has a launch and a nice boardwalk nature trail that kids (if you have them) will enjoy. You can also put in at the bridge and down at the lakefront launch where the Tchefuncte meets Lake P. Watch out for St. Tammany boat deputies in the wake zones...they're brutal.

As others have mentioned, there's a ramp at the park. Day use fee is $2/head (for over 3 years old and under 62, I think). I think you're allowed 2 cars and 6 people per campsite. If you're in the overnight group I don't think you'll have to pay the day use fee.

You can't dock at the boardwalk along the river. There are some slips back by the launch you can use.

If you have a friend at Smoketree Landscaping on Hwy 22 btwn the park and the bridge, they have a dip launch.

There's a raggedy free launch at the 22 bridge. Parking is tight.

There's a pay launch, ample parking and fuel at Marina del Rey.

There's a puclic launch at the end of Lake Rd, but you need a City of Madisonville permit to park. It's just a few dollars per year.

Private property, I'm almost certain. It was used as an equipment staging area for a while during the seawall construction and got fenced then. (You used to be able to drive to or fish from the west end of that spit of land looking towards the lighthouse.)
After the construction was complete, they put in permanent footings and piers on the houses. The "big" house was on cribbing for a long time. The house to the right/north is new construction. Or new to that location, at least. If you look around the parking lot and the first 1/4 mile or so going out, there's a wire fence with "posted" signs. I'm pretty sure it's all private ownership.

Speaking of signs, look about 15' up the light poles in the lot. There are signs about the parking regulations up there. I don't know how strictly it's enforced, but they've been up there at least a year or two. Sometime after the new seawall was built after Isaac, which was Aug., 2012.