State radon data hub

Ohio radon levels, county by county

88 Ohio counties have published radon test data. Ranked worst-first below — the median county sees 53.3% of home tests reach the EPA action level of 4 pCi/L. Deep-dive pages (data + geology + housing stock) exist for 9 counties so far; more ship as coverage expands.

Costs, licensing, and how to read a quote: the Ohio mitigation cost guide. Instant county lookup: radon by ZIP.

#	County	% tests ≥ 4 pCi/L	Tests (10-yr)	EPA zone
1	Pickaway	81.4%	154	1
2	Fairfield	76.8%	1,004	1
3	Logan	73.6%	487	1
4	Delaware	72.2%	3,158	1
5	Knox	72%	987	1
6	Franklin	71.9%	13,807	1
7	Auglaize	71.2%	113	1
8	Licking	71.2%	3,431	1
9	Champaign	71.1%	412	1
10	Madison	67.4%	423	1
11	Ross	67.1%	251	1
12	Tuscarawas	66.4%	480	1
13	Marion	65.3%	192	1
14	Miami	65.2%	513	1
15	Morrow	65%	143	1
16	Holmes	64.2%	58	1
17	Darke	63.7%	189	1
18	Ashland	62.9%	276	1
19	Preble	62.7%	133	1
20	Richland	62.2%	998	1
21	Henry	61.8%	35	2
22	Wayne	61.8%	950	1
23	Union	60.2%	968	1
24	Shelby	60.1%	206	1
25	Stark	60.1%	3,174	1
26	Putnam	59.6%	74	2
27	Crawford	59.5%	175	1
28	Huron	59.4%	692	1
29	Sandusky	59.2%	630	2
30	Coshocton	58.9%	95	1
31	Seneca	58.9%	511	1
32	Greene	58.6%	1,785	1
33	Fayette	58.3%	12	1
34	Monroe	58.3%	40	2
35	Mercer	57.7%	98	1
36	Clark	57.5%	1,123	1
37	Carroll	57.4%	368	1
38	Allen	56.7%	185	1
39	Highland	56.7%	53	2
40	Muskingum	56.3%	339	1
41	Pike	56.1%	33	1
42	Erie	54.5%	1,436	2
43	Butler	54.3%	1,552	1
44	Van Wert	53.8%	18	1
45	Hocking	53.3%	41	2
46	Warren	52.5%	2,076	1
47	Clinton	52.4%	80	1
48	Montgomery	50.3%	2,223	1
49	Adams	50%	19	1
50	Clermont	50%	1,168	2
51	Harrison	50%	37	1
52	Jefferson	49.8%	240	1
53	Columbiana	49.1%	537	1
54	Perry	48.9%	78	1
55	Defiance	48.6%	55	2
56	Brown	47.1%	51	2
57	Wyandot	46.3%	224	1
58	Hancock	46.2%	1,221	1
59	Wood	45.5%	1,469	2
60	Lorain	45.4%	2,937	2
61	Belmont	45.2%	723	1
62	Fulton	45.2%	56	2
63	Guernsey	44.4%	93	1
64	Medina	43.4%	1,942	2
65	Hardin	43.3%	42	1
66	Williams	42.9%	23	2
67	Jackson	41.7%	35	2
68	Ottawa	40.3%	479	2
69	Lucas	40.2%	1,752	2
70	Portage	39.3%	1,561	2
71	Summit	38.7%	6,002	1
72	Athens	38.1%	181	2
73	Washington	38.1%	290	2
74	Scioto	37%	48	2
75	Hamilton	34.7%	3,085	1
76	Trumbull	34.6%	377	2
77	Ashtabula	34.4%	282	2
78	Gallia	33.3%	16	2
79	Noble	31%	34	2
80	Lawrence	30.3%	53	2
81	Morgan	30%	9	2
82	Lake	27.2%	2,194	2
83	Vinton	25%	4	2
84	Geauga	23.4%	1,382	2
85	Mahoning	23.4%	556	2
86	Paulding	23.1%	12	2
87	Cuyahoga	21.7%	8,861	2
88	Meigs	20%	16	2

Source: CDC EPHT (labs), 2008–2017; county rank by share of tests at or above 4 pCi/L (counties with too few reported tests are excluded — absence of data is not absence of radon). Zones: EPA Map of Radon Zones. Full sourcing on the methodology page.