Lake Iamonia - Northern Leon County
Here's Lake Iamonia you asked about. (the prairie lake you saw)...  you all and Peg drove with us up U.S. 319 and went to the boat landing at the end of Lake Iamonia Rd. on the north side. A red dot indicates where we were (a bait store is there). 
We then went west on County Road 12 to N. Meridian Rd. and followed it south. Another red dot indicates the other boat ramp we were at. The last red dot is our house.

Lakes here aren't real deep. Iamonia's maximum depth seems to be to be around 20-30 feet. especially at the sinkholes which feed it from below. 
 

Iamonia measures 6.5 miles in length by 2 mi. wide at its widest point from map details and covers 5757 surface acres.

From research I found the lake is shallowest at the west end. 

Links
Fishing Iamonia
Good County Map

Lake Monkey Business shown on the map is inside our park here. This is where you guys walked out onto a small island with picnic tables.


 
Bradley's Country Store
Just in case you wanted to see where you went 
again for the 2nd time. Here it is.
We always enjoy it. It's the red dot!

 
The pond right across from Bradley's

Both are clickable links.