Two canoes crossing open water between forested points in the Boundary Waters

Updated August 2026

Biggest Lake in Ohio: Grand Lake St. Marys (13,500 acres)

Grand Lake St. Marys is Ohio's largest inland lake per the Ohio DNR (Division of Parks & Watercraft). Below: 50 Ohio lakes ranked by surface area.

The largest lake in Ohio is Grand Lake St. Marys at 13,500 acres , in Mercer and Auglaize County, according to the Ohio DNR (Division of Parks & Watercraft). Lake Erie is a Great Lake shared with Michigan, Pennsylvania, New York and Ontario, Canada; Ohio's Lake Erie waters are orders of magnitude larger than any inland lake, so the answer is stated as Ohio's largest INLAND lake. Pymatuning Reservoir (17,088 acres) is also larger but straddles the Ohio-Pennsylvania line.

Grand Lake St. Marys isn't in our water-quality index — we grade lakes with enough EPA Water Quality Portal samples to score, which leaves out many large reservoirs and border waters. The ranking below covers the 50 Ohio lakes we do grade, led by Mosquito Creek Lake.

Source: Ohio DNR (Division of Parks & Watercraft) (2026-07-30). The table below ranks the Ohio lakes in our own index by surface area.

Lakes with area data

7,016

Largest (acres)

696

Median of top 50

5/50

Reservoirs (vs natural)

Reading Ohio's size profile

Ohio's largest lake by surface area is Mosquito Creek Lake in Trumbull County, spanning 7,016 acres. Most of Ohio's biggest waters are natural basins left by glaciers, with stable shorelines and deep main basins.

Surface area is a poor proxy for water quality on its own — a large lake can hold a clean, deep core and a nutrient-loaded bay at the same time. Each lake below links to its full report card with grade, clarity, depth, and EPA impairment status. Area figures come from state DNR surveys and the USACE National Inventory of Dams; grades come from EPA and state monitoring data.

The 50 biggest lakes in Ohio by surface area

#	Lake	County	Surface area	Max depth	Grade
1	Mosquito Creek Lake	Trumbull	7,016 acres	-	NR
2	Dunns Pond	Logan	5,069 acres	-	NR
3	Berlin Lake	Portage	3,591 acres	-	NR
4	Caesar Creek Lake	Warren	2,830 acres	-	D
5	Salt Fork Lake	Guernsey	2,792 acres	-	NR
6	Crane Lake	Fairfield	2,757 acres	-	NR
7	Michael J Kirwan Reservoir	Portage	2,605 acres	-	NR
8	Pleasant Hill Reservoir	Richland	2,600 acres	-	NR
9	Piedmont Lake	Belmont	2,275 acres	-	NR
10	Rocky Fork Lake	Highland	1,990 acres	-	NR
11	William H Harsha Lake	Clermont	1,975 acres	-	NR
12	Meander Creek Reservoir	Mahoning	1,882 acres	-	NR
13	Lake Milton	Mahoning	1,656 acres	-	NR
14	Clendening Lake	Harrison	1,640 acres	-	NR
15	Atwood Lake	Carroll	1,515 acres	-	NR
16	Akron City Reservoir	Geauga	1,422 acres	-	NR
17	Charles Mill Reservoir	Ashland	1,350 acres	-	NR
18	Dillon Lake	Muskingum	1,307 acres	-	NR
19	Deer Creek Lake	Pickaway	1,270 acres	-	NR
20	Paint Creek Lake	Highland	1,162 acres	-	NR
21	Delaware Lake	Delaware	1,122 acres	-	NR
22	Clear Fork Reservoir	Morrow	1,024 acres	-	NR
23	Leesville Lake	Carroll	1,000 acres	-	NR
24	Lake Loramie	Shelby	854 acres	-	NR
25	Mogadore Reservoir	Portage	761 acres	-	NR
26	Cowan Lake	Clinton	696 acres	-	NR
27	Lake Rockwell	Portage	662 acres	-	NR
28	Nimisila Reservoir	Summit	654 acres	-	NR
29	Killdeer Wildlife Pond Number Three	Wyandot	654 acres	-	NR
30	Burr Oak Reservoir	Athens	632 acres	-	NR
31	Findlay Upground Reservoir Number Two	Hancock	629 acres	-	NR
32	Acton Lake	Preble	590 acres	-	NR
33	Evans Lake	Mahoning	562 acres	-	NR
34	Lake Mohawk	Carroll	506 acres	-	NR
35	Apple Valley Lake	Knox	499 acres	-	NR
36	Pine Lake	Mahoning	479 acres	-	NR
37	Knox Lake	Knox	464 acres	-	NR
38	Rex Lake	Summit	454 acres	-	NR
39	Lake Roaming Rock	Ashtabula	451 acres	-	NR
40	Wills Creek Lake	Coshocton	413 acres	-	NR
41	East Branch Reservoir	Geauga	394 acres	-	NR
42	Wingfoot Lake	Portage	387 acres	-	NR
43	Kiser Lake	Champaign	387 acres	-	NR
44	Aurora Pond	Portage	345 acres	-	NR
45	Lake White	Pike	345 acres	-	NR
46	The Bogs	Sandusky	344 acres	-	NR
47	Portage Lakes	Summit	336 acres	-	NR
48	Chippewa Lake	Medina	330 acres	-	NR
49	Guilford Lake	Columbiana	328 acres	-	NR
50	Lake Rupert	Vinton	322 acres	-	NR

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Frequently Asked Questions

What is the largest lake in Ohio?

Grand Lake St. Marys, at 13,500 acres, in Mercer and Auglaize County. Lake Erie is a Great Lake shared with Michigan, Pennsylvania, New York and Ontario, Canada; Ohio's Lake Erie waters are orders of magnitude larger than any inland lake, so the answer is stated as Ohio's largest INLAND lake. Pymatuning Reservoir (17,088 acres) is also larger but straddles the Ohio-Pennsylvania line. Source: Ohio DNR (Division of Parks & Watercraft), 2026-07-30.

How is lake surface area measured?

Surface area comes from state DNR lake surveys and, for reservoirs, US Army Corps of Engineers (USACE) National Inventory of Dams records. Area is reported in acres at normal pool level. Reservoirs rise and fall with management and drought, so their listed area is the long-term normal rather than a single-day reading.

Are Ohio's largest lakes natural or reservoirs?

Of the top 50 Ohio lakes by area, 5 sit on a dammed river (reservoirs) and 45 are natural basins. Glacial states (MN, WI, MI, NY) skew natural; plains and southern states (MO, IA, ND, OH) skew toward reservoirs built for water supply, flood control, and recreation.

Do larger lakes have better water quality?

Not reliably. Quality varies more within a big lake than between lakes — a large lake can have a clean, deep main basin and a murky, algae-prone bay fed by a tributary, so one grade can mask wide swings. Depth, watershed land use, and how fast the lake flushes matter far more than raw surface area.

How big is the typical Ohio lake in this ranking?

Across the top 50 Ohio lakes by surface area, the median is 696 acres (Cowan Lake). This list is biased toward the biggest waters; the typical Ohio lake is far smaller.

Where to stay near Ohio's largest lakes

Planning a trip? Jump to live cabin, resort, and hotel availability near Ohio's biggest lakes.

Deepest lakes in Ohio →Largest lakes (all states) →All Ohio lakes →