Exhibit 5(a)

NORTH POINT • 901 LAKESIDE AVENUE • CLEVELAND, OHIO 44114.1190

TELEPHONE: +1.216.586.3939 • FACSIMILE: +1.216.579.0212

March 6, 2018    

FirstEnergy Corp.

76 South Main Street

Akron, Ohio 44308

Re:    Registration Statement on Form S-3 Filed by FirstEnergy Corp.

Ladies and Gentlemen:

We have acted as counsel for FirstEnergy Corp., an Ohio corporation (the “Company”), in connection with the authorization of the possible issuance and sale from time to time, on a delayed basis, by the Company of an indeterminate amount of: (i) shares of common stock, par value $0.10 per share, of the Company (the “Common Stock”); (ii) shares of preferred stock, par value $100 per share, of the Company (the “Preferred Stock”), in one or more series; (iii) debt securities of the Company (the “Debt Securities”), in one or more series; and (iv) warrants to purchase Common Stock, Preferred Stock, Debt Securities, securities of third parties or certain other rights, or a combination of the foregoing (the “Warrants”), in each case, as contemplated by the Registration Statement on Form S-3 to which this opinion has been filed as an exhibit (the “Registration Statement”). The Common Stock, the Preferred Stock, the Debt Securities and the Warrants are collectively referred to herein as the “Securities.” The Securities may be offered and sold from time to time pursuant to Rule 415 under the Securities Act of 1933 (the “Securities Act”). The Debt Securities are to be issued under an Indenture, dated as of November 15, 2001 (as supplemented from time to time, the “Indenture”), between the Company and The Bank of New York Mellon Trust Company, N.A., as successor trustee (the “Trustee”).

In connection with the opinions expressed herein, we have examined such documents, records and matters of law as we have deemed relevant or necessary for purposes of such opinions. Based on the foregoing, and subject to the further limitations, qualifications and assumptions set forth herein, we are of the opinion that:

1. The shares of Common Stock, upon receipt by the Company of such lawful consideration therefor having a value not less than the par value thereof as the Company’s Board of Directors (or an authorized committee or subcommittee thereof) may determine, will be validly issued, fully paid and nonassessable.

2. The shares of Preferred Stock, upon receipt by the Company of such lawful consideration therefor having a value not less than the par value thereof as the Company’s Board of Directors (or an authorized committee or subcommittee thereof) may determine, will be validly issued, fully paid and nonassessable.

FirstEnergy Corp.

March 6, 2018

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3. The Debt Securities, when executed by the Company and authenticated by the Trustee in accordance with the Indenture, issued and sold in accordance with the Registration Statement and delivered to the purchaser or purchasers thereof against receipt by the Company of such lawful consideration therefor as the Company’s Board of Directors (or an authorized committee or subcommittee thereof) may determine, will constitute valid and binding obligations of the Company.

4. The Warrants, upon receipt by the Company of such lawful consideration therefor as the Company’s Board of Directors (or an authorized committee or subcommittee thereof) may determine, will constitute valid and binding obligations of the Company.

In rendering the foregoing opinions, we have assumed that: (i) the Registration Statement, and any amendments thereto, will have become effective (and will remain effective at the time of issuance of any Securities thereunder); (ii) a prospectus supplement describing each class or series of Securities offered pursuant to the Registration Statement, to the extent required by applicable law and relevant rules and regulations of the Securities and Exchange Commission (the “Commission”), will be timely filed with the Commission; (iii) the definitive terms of each class or series of Securities will have been established in accordance with the authorizing resolutions adopted by the Company’s Board of Directors (or an authorized committee or subcommittee thereof), the Company’s Amended Articles of Incorporation, as amended (the “Amended Articles of Incorporation”), and applicable law; (iv) the Company will issue and deliver the Securities in the manner contemplated by the Registration Statement and any Securities that consist of shares of capital stock will have been authorized and reserved for issuance, in each case within the limits of the then remaining authorized but unissued and unreserved amounts of such capital stock; (v) the resolutions authorizing the Company to issue, offer and sell the Securities will have been adopted by the Company’s Board of Directors (or an authorized committee or subcommittee thereof) and will be in full force and effect at all times at which the Securities are offered or sold by the Company; (vi) all Securities will be issued in compliance with applicable federal and state securities laws; and (vii) any Warrant Agreement (as defined below) will be governed by and construed in accordance with the laws of the State of New York and will constitute a valid and binding obligation of each party thereto other than the Company.

With respect to any Securities consisting of Preferred Stock, we have further assumed that the Company will issue and deliver the shares of the Preferred Stock being issued and delivered after the filing with the Secretary of State of the State of Ohio of a certificate of amendment to the Amended Articles of Incorporation, approved by us, establishing the designations, preferences and rights of the class or series of the Preferred Stock being issued and delivered.

With respect to any Securities consisting of any series of Debt Securities, we have further assumed that: (i) the Indenture is, and any supplemental indenture will be, a valid and binding obligation of the Trustee; (ii) all terms of the Debt Securities not provided for in the Indenture will have been established in accordance with the provisions of the Indenture and reflected in appropriate documentation approved by us and, if applicable, executed and delivered by the

FirstEnergy Corp.

March 6, 2018

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Company and the Trustee; and (iii) the Debt Securities will be executed, authenticated, issued and delivered in accordance with the provisions of the Indenture.

With respect to any Securities consisting of Warrants, we have further assumed that: (i) the warrant agreement, approved by us, relating to the Warrants (the “Warrant Agreement”) to be entered into between the Company and an entity selected by the Company to act as the warrant agent (the “Warrant Agent”) will have been authorized, executed and delivered by the Company and the Warrant Agent; and (ii) the Warrants will be authorized, executed and delivered by the Company and the Warrant Agent in accordance with the provisions of the Warrant Agreement.

The opinions expressed herein are limited by bankruptcy, insolvency, reorganization, fraudulent transfer and fraudulent conveyance, voidable preference, moratorium or other similar laws and related regulations and judicial doctrines from time to time in effect relating to or affecting creditors’ rights generally, and by general equitable principles and public policy considerations, whether such principles and considerations are considered in a proceeding at law or in equity.

As to facts material to the opinions and assumptions expressed herein, we have relied upon oral or written statements and representations of officers and other representatives of the Company and others. The opinions expressed herein are limited to the laws of the State of New York and the laws of the State of Ohio, in each case as currently in effect, and we express no opinion as to the effect of the laws of any other jurisdiction.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Registration Statement and to the reference to Jones Day under the caption “Legal Matters” in the prospectus constituting a part of such Registration Statement. In giving such consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission promulgated thereunder.

Very truly yours,

/s/ Jones Day