You need a State Park sticker ($24 for annual or $6 for daily), an ORV sticker ($16.95), a flag ($15-$24) and a flag bracket ($10-$20). And if you going on the weekend before Labor day, you need a voucher for each day. These are free but need to be picked up at the voucher center. The flag and bracket can be picked up at several local shops. You'll see them outside the shops.
Here's the DNR's Silver Lake info page.
Project: Lil' Laff - 1990 Jeep YJ Laredo 4.2 I-6
Weber 38 DGES, Skyjacker 4" Lift, AGR Super Box 2 & Super Pump, SYE, TJ Flares, Tom Wood's Driveshafts
2010 Jeep JK Islander 3.8 V6 - Stock