Pennsylvania radon levels by county

Computed 2026-10-11 from PA DEP's Radon Test Results, September 1986 - Current (PA Open Data Portal, public domain). Statewide, 37% of 2,644,033 basement tests were at or above 4 pCi/L. These are tests reported to DEP, not a random survey: repeat and post-mitigation tests are included. Basement readings usually run higher than living-floor readings.

For EPA's county zone classifications, see the EPA Map of Radon Zones. EPA recommends fixing a home at 4 pCi/L or more and considering it between 2 and 4 pCi/L (EPA).

Rank	County	Basement tests	Median (pCi/L)	% basement ≥ 4	% first floor ≥ 4	Certified firms
1	Fulton	707	7.6	70%	52%	0
2	Juniata	1,802	5.6	62%	45%	0
3	Perry	5,953	6.0	61%	39%	1
4	Lebanon	26,763	6.3	60%	37%	4
5	Mifflin	3,773	5.5	59%	53%	1
6	Franklin	20,850	5.2	59%	37%	5
7	York	81,840	4.9	56%	33%	8
8	Centre	39,814	5.2	56%	42%	4
9	Jefferson	4,562	4.7	56%	28%	0
10	Schuylkill	18,758	4.9	56%	30%	5
11	Bedford	4,040	4.7	55%	23%	1
12	Cumberland	76,621	4.8	55%	37%	6
13	Lancaster	109,372	4.7	55%	39%	9
14	Armstrong	4,627	4.3	53%	24%	2
15	Huntingdon	3,984	4.3	53%	25%	3
16	Clearfield	10,793	4.3	53%	27%	1
17	Carbon	9,429	4.4	53%	23%	2
18	Potter	1,636	4.1	51%	20%	0
19	Dauphin	67,255	4.1	51%	24%	9
20	Columbia	10,285	4.1	51%	24%	2
21	Berks	78,443	4.0	51%	37%	9
22	Snyder	4,749	4.0	50%	20%	2
23	Bradford	4,704	3.8	49%	27%	1
24	Cameron	439	3.9	49%	40%	0
25	Forest	261	3.6	49%	21%	0
26	Beaver	30,533	3.8	48%	33%	6
27	Northampton	78,045	3.7	48%	26%	7
28	Elk	3,519	3.8	48%	26%	1
29	Clarion	3,576	3.8	48%	20%	0
30	Warren	3,863	3.7	47%	26%	1
31	Lehigh	85,538	3.6	47%	29%	11
32	Butler	45,628	3.6	47%	30%	12
33	Northumberland	10,034	3.6	46%	16%	1
34	Monroe	39,824	3.6	46%	17%	11
35	Venango	5,018	3.6	46%	22%	2
36	Lycoming	15,471	3.6	46%	21%	2
37	Indiana	9,119	3.6	46%	24%	2
38	Clinton	4,724	3.5	46%	19%	2
39	Union	8,075	3.5	45%	19%	1
40	Adams	16,668	3.4	44%	17%	6
41	Somerset	5,585	3.4	44%	22%	1
42	Cambria	16,349	3.4	43%	22%	4
43	Wyoming	4,072	3.4	43%	14%	0
44	Blair	17,390	3.2	43%	22%	3
45	Tioga	3,242	3.2	42%	15%	1
46	Montour	4,297	3.2	42%	20%	0
47	Susquehanna	3,719	3.2	41%	13%	1
48	Westmoreland	66,800	3.2	40%	25%	17
49	Sullivan	622	3.1	39%	16%	0
50	Pike	21,604	2.9	38%	13%	7
51	Lawrence	9,105	3.1	38%	23%	2
52	Mercer	9,723	2.9	35%	13%	0
53	Crawford	5,647	2.8	35%	11%	3
54	Washington	38,759	2.9	34%	21%	7
55	Allegheny	311,850	2.7	34%	21%	44
56	Greene	1,562	2.8	34%	16%	0
57	Fayette	7,625	2.9	34%	16%	3
58	Chester	212,529	2.4	31%	20%	18
59	Bucks	199,252	2.5	31%	14%	19
60	Luzerne	55,278	2.4	31%	11%	13
61	Wayne	14,704	2.4	29%	11%	4
62	Erie	41,146	2.2	28%	14%	6
63	Montgomery	296,621	2.4	28%	12%	29
64	Lackawanna	36,863	2.3	28%	9%	9
65	McKean	1,583	2.1	27%	8%	0
66	Delaware	151,566	2.0	20%	8%	12
67	Philadelphia	155,445	1.7	12%	5%	10