Reference

Ohio API county codes

Every Ohio API well number starts with 34, the state code. The next three digits are the county code, one of the 88 listed below, so a number beginning 34-001 belongs to a well in Adams County.

To decode a whole number, including the sidetrack and completion digits, paste it into the API well number decoder.

How to read a Ohio API number

34State: Ohio

001County: Adams

12345Well, unique within the county

The first ten digits identify one well. Two more digits can follow for a sidetrack, and two after that for a later completion. The county is the one where the well starts at the surface, so a horizontal well that crosses a county line keeps its surface county's code. A few state regulators assign the producing county instead, so the state record is the final word on a well near a boundary.

All 88 Ohio counties

County code	County	API numbers start
001	Adams	34-001-
003	Allen	34-003-
005	Ashland	34-005-
007	Ashtabula	34-007-
009	Athens	34-009-
011	Auglaize	34-011-
013	Belmont	34-013-
015	Brown	34-015-
017	Butler	34-017-
019	Carroll	34-019-
021	Champaign	34-021-
023	Clark	34-023-
025	Clermont	34-025-
027	Clinton	34-027-
029	Columbiana	34-029-
031	Coshocton	34-031-
033	Crawford	34-033-
035	Cuyahoga	34-035-
037	Darke	34-037-
039	Defiance	34-039-
041	Delaware	34-041-
043	Erie	34-043-
045	Fairfield	34-045-
047	Fayette	34-047-
049	Franklin	34-049-
051	Fulton	34-051-
053	Gallia	34-053-
055	Geauga	34-055-
057	Greene	34-057-
059	Guernsey	34-059-
061	Hamilton	34-061-
063	Hancock	34-063-
065	Hardin	34-065-
067	Harrison	34-067-
069	Henry	34-069-
071	Highland	34-071-
073	Hocking	34-073-
075	Holmes	34-075-
077	Huron	34-077-
079	Jackson	34-079-
081	Jefferson	34-081-
083	Knox	34-083-
085	Lake	34-085-
087	Lawrence	34-087-
089	Licking	34-089-
091	Logan	34-091-
093	Lorain	34-093-
095	Lucas	34-095-
097	Madison	34-097-
099	Mahoning	34-099-
101	Marion	34-101-
103	Medina	34-103-
105	Meigs	34-105-
107	Mercer	34-107-
109	Miami	34-109-
111	Monroe	34-111-
113	Montgomery	34-113-
115	Morgan	34-115-
117	Morrow	34-117-
119	Muskingum	34-119-
121	Noble	34-121-
123	Ottawa	34-123-
125	Paulding	34-125-
127	Perry	34-127-
129	Pickaway	34-129-
131	Pike	34-131-
133	Portage	34-133-
135	Preble	34-135-
137	Putnam	34-137-
139	Richland	34-139-
141	Ross	34-141-
143	Sandusky	34-143-
145	Scioto	34-145-
147	Seneca	34-147-
149	Shelby	34-149-
151	Stark	34-151-
153	Summit	34-153-
155	Trumbull	34-155-
157	Tuscarawas	34-157-
159	Union	34-159-
161	Van Wert	34-161-
163	Vinton	34-163-
165	Warren	34-165-
167	Washington	34-167-
169	Wayne	34-169-
171	Williams	34-171-
173	Wood	34-173-
175	Wyandot	34-175-

County names are the US Census names for these codes. The API standard does not promise the two match, so we checked them against state well records. Across 35 states, where this table names a county it matched the one the agency recorded on 85,091 of 85,100 wells. Offshore state and federal waters use their own pseudo-county codes, which are not listed here.

Finding the well itself

The API number stops at the county. It does not hold the well's coordinates, lease, survey section or operator. Those sit in the well record, which you find by searching the full number in the state agency's system. In Ohio that is the ODNR well information report, run by the Ohio Department of Natural Resources (ODNR).

For what the Ohio public records hold in total, see the Ohio oil and gas data summary.

Frequently asked questions

What is the API state code for Ohio?

34. API state codes run alphabetically from 01 for Alabama to 49 for Wyoming, then 50 for Alaska and 51 for Hawaii. They are not the Census FIPS state codes, which is a common source of wrong lookups.

How do I find the county from a Ohio API number?

Read digits three to five and find them in the table on this page. In 34-001-12345, the county code is 001, which is Adams County. If the code is missing from the table, it is usually an offshore area rather than an onshore county.

Does a Ohio API number give the well's exact location?

No. The number stops at the county. Coordinates, the lease and the survey location are in the well record held by the state agency, which you search with the full API number.

Every Ohio well, on one map

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State codes: American Petroleum Institute Bulletin D12A well numbering standard. County names: US Census county FIPS names, checked against state well records. Reference generated 2026-09-24.

How to cite this page

Sources: American Petroleum Institute Bulletin D12A well numbering standard; US Census county FIPS codes.

TetraSoft. (2026). Ohio API county codes. Reference generated 2026-09-24. https://tetrasoftco.com/tools/api-county-codes/ohio/