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

Updated August 2026

Biggest Inland 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 inland 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.

See our Grand Lake St. Marys water-quality readings —

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 and reaching 39.6 ft deep. 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 page with nutrient readings, clarity, depth, and EPA impairment status. Area figures come from state DNR surveys and the USACE National Inventory of Dams; water-quality readings come from EPA and state monitoring data.

The 50 biggest lakes in Ohio by surface area

#	Lake	County	Surface area	Max depth
1	Mosquito Creek Lake	Trumbull	7,016 acres	39.6 ft
2	Dunns Pond	Logan	5,069 acres	13.3 ft
3	Berlin Lake	Portage	3,591 acres	55.8 ft
4	Caesar Creek Lake	Warren	2,830 acres	-
5	Salt Fork Lake	Guernsey	2,792 acres	36 ft
6	Crane Lake	Fairfield	2,757 acres	15.5 ft
7	Michael J Kirwan Reservoir	Portage	2,605 acres	-
8	Pleasant Hill Reservoir	Richland	2,600 acres	-
9	Piedmont Lake	Belmont	2,275 acres	32.1 ft
10	Rocky Fork Lake	Highland	1,990 acres	42.5 ft
11	William H Harsha Lake	Clermont	1,975 acres	119.6 ft
12	Meander Creek Reservoir	Mahoning	1,882 acres	-
13	Lake Milton	Mahoning	1,656 acres	35.7 ft
14	Clendening Lake	Harrison	1,640 acres	36.9 ft
15	Atwood Lake	Carroll	1,515 acres	33.1 ft
16	Akron City Reservoir	Geauga	1,422 acres	26.2 ft
17	Charles Mill Reservoir	Ashland	1,350 acres	-
18	Dillon Lake	Muskingum	1,307 acres	31.8 ft
19	Deer Creek Lake	Pickaway	1,270 acres	39.3 ft
20	Paint Creek Lake	Highland	1,162 acres	41.6 ft
21	Delaware Lake	Delaware	1,122 acres	32.9 ft
22	Clear Fork Reservoir	Morrow	1,024 acres	-
23	Leesville Lake	Carroll	1,000 acres	-
24	Lake Loramie	Shelby	854 acres	-
25	Mogadore Reservoir	Portage	761 acres	25 ft
26	Cowan Lake	Clinton	696 acres	35.9 ft
27	Lake Rockwell	Portage	662 acres	-
28	Nimisila Reservoir	Summit	654 acres	30 ft
29	Killdeer Wildlife Pond Number Three	Wyandot	654 acres	-
30	Burr Oak Reservoir	Athens	632 acres	35.2 ft
31	Findlay Upground Reservoir Number Two	Hancock	629 acres	27.1 ft
32	Acton Lake	Preble	590 acres	30.8 ft
33	Evans Lake	Mahoning	562 acres	-
34	Lake Mohawk	Carroll	506 acres	-
35	Apple Valley Lake	Knox	499 acres	-
36	Pine Lake	Mahoning	479 acres	-
37	Knox Lake	Knox	464 acres	39.1 ft
38	Rex Lake	Summit	454 acres	-
39	Lake Roaming Rock	Ashtabula	451 acres	-
40	Wills Creek Lake	Coshocton	413 acres	13.1 ft
41	East Branch Reservoir	Geauga	394 acres	16.4 ft
42	Wingfoot Lake	Portage	387 acres	-
43	Kiser Lake	Champaign	387 acres	13.4 ft
44	Aurora Pond	Portage	345 acres	-
45	Lake White	Pike	345 acres	30 ft
46	The Bogs	Sandusky	344 acres	-
47	Portage Lakes	Summit	336 acres	61.2 ft
48	Chippewa Lake	Medina	330 acres	-
49	Guilford Lake	Columbiana	328 acres	23 ft
50	Lake Rupert	Vinton	322 acres	23 ft

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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 reading 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.

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