EX-4.2





 Exhibit 4.2 

[FORM OF NOTE] 
 Unless this
Security is presented by an authorized representative of The Depository Trust Company (55 Water Street, New York, New York) to the issuer or its agent for registration of transfer, exchange or payment, and any Security issued upon registration of
transfer of, or in exchange for, or in lieu of, this Security is registered in the name of Cede & Co. or such other name as requested by an authorized representative of The Depository Trust Company and any payment hereon is made to
Cede & Co., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL since the registered owner hereof, Cede & Co., has an interest herein. 

AON CORPORATION 
 2.200%
Senior Notes due 2022 
 Guaranteed by Aon plc 
  

			
	No. 	  	$                    

 CUSIP No. 037389 BD4 

AON CORPORATION 
 Aon
Corporation, a Delaware corporation (herein called the “Company,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The
Depository Trust Company, or registered assigns, the principal sum of                      DOLLARS
($            ) on November 15, 2022 and, subject to Section 16.05 of said Indenture, to pay interest thereon from November 15, 2019 or from the most recent Interest
Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on each May 15 and November 15, commencing May 15, 2020 (each, an “Interest Payment Date”), at the rate of 2.200% per annum, until
the principal hereof is paid or made available for payment. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security
(or one or more predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the May 1 or November 1 (whether or not a Business Day), as the case may be, immediately preceding
such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or
more predecessor Securities) is registered at the close of business on a subsequent record date for the payment of such defaulted interest established by the Company, notice whereof shall be given to Holders of Securities of this series not less
than 15 days prior to such subsequent record date, such record date to be not less than 5 days preceding the date of payment of such defaulted interest, or be paid at any time in any other lawful manner not inconsistent with the requirements of any
securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture. 












 Payment of the principal of (and premium, if any) and any such interest on this Security
will be made at the office or agency of the Company maintained for that purpose in the City of Chicago or the Borough of Manhattan, The City of New York, in such coin or currency of the United States of America as at the time of payment is legal
tender for payment of public and private debts; provided, however, that at the option of the Company payment of interest may be made by wire transfer, other electronic means or mailing checks to the address of the Holder entitled
thereto as such address shall appear in the Security Register. 
 The Securities of this series are subject to redemption and repurchase at
the option of the Company prior to the stated maturity as described in the Indenture and on the reverse hereof. 
 Reference is hereby made
to the further provisions of this Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place. 

Unless the certificate of authentication hereon has been executed by the Trustee referred to herein by manual signature, this Security shall
not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose. 












 IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed. 

Dated: November 15, 2019 
  

			
	AON CORPORATION
		
	By:	 	              

		 	Name: Paul Hagy
		 	Title: Senior Vice President and Treasurer


  

			
	 Attest:

	
	  

	 Name: Molly Johnson

	 Title: Vice President and Secretary














 This is one of the Securities of the series designated therein referred to in the
within-mentioned Indenture. 
  

											
		 		 		 		 	 THE BANK OF NEW YORK MELLON TRUST COMPANY, N.A., as Trustee

						
	Dated: November 15, 2019	 		 		 		 	By:	 	              

		 		 		 		 		 	Authorized Officer













 This Security is one of a duly authorized series of securities of the Company entitled
“2.200% Senior Notes due 2022” (herein called the “Securities”) issued and to be issued in one or more series under the Indenture dated as of December 3, 2018 and an officers’ certificate dated as of November 15,
2019 (together, the “Indenture”), between the Company, the Guarantor and The Bank of New York Mellon Trust Company, N.A., as Trustee (herein called the “Trustee,” which term includes any successor trustee under the Indenture), to
which Indenture and all indentures supplemental thereto reference is hereby made for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities and of
the terms upon which the Securities are, and are to be, authenticated and delivered. The Securities of this series will initially be issued in the aggregate principal amount of $500,000,000. The Company may, from time to time, without the
written consent of or notice to holders of the Securities of this series, create and issue under the Indenture additional securities having the same terms and conditions as the Securities of this series (other than the issue date, the issue price
and, to the extent applicable, the first date from which interest on such additional securities shall accrue and the first interest payment date for such additional securities) and such additional securities shall be consolidated with and form a
single series with the Securities of this series. 
 The Company may redeem the Securities of this series, in whole at any time, or in part
from time to time, at the Company’s option, at a price equal to the greater of (1) 100% of the principal amount of the Securities to be redeemed and (2) the sum of the present values of the remaining scheduled payments of principal
and interest thereon (not including any portion of such payments of interest accrued as of the redemption date), discounted to the date of redemption on a semi-annual basis (assuming a 360-day year consisting
of twelve 30-day months), at a rate equal to the sum of the applicable Treasury Rate (as defined below), plus 10 basis points, plus, in each case, accrued and unpaid interest thereon to but excluding the
redemption date (each such redemption being an “Optional Redemption”). 
 If the Company has given notice of Optional Redemption
as provided herein and in the Indenture and funds for the redemption of any Securities of this series called for Optional Redemption have been made available on the applicable redemption date, such Securities will cease to bear interest on the date
fixed for redemption. Thereafter, the only right of the Holders of such Securities will be to receive payment of the applicable redemption price. 

The Company will prepare and send a notice of an Optional Redemption to each Holder of Securities to be redeemed by first-class mail at least
30 and not more than 90 calendar days prior to the date fixed for such Optional Redemption. On and after the redemption date for an Optional Redemption, interest will cease to accrue on the Securities called for redemption (unless the Company
defaults in the payment of the redemption price). 
 “Comparable Treasury Issue” means the United States Treasury security
selected by the Quotation Agent as having a maturity comparable to the remaining term of the Securities to be redeemed that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of
corporate debt securities of comparable maturity to the remaining term of the Securities. 












 “Comparable Treasury Price” means, with respect to any redemption date,
(i) the average of three Reference Treasury Dealer Quotations for such redemption date, after excluding the highest and lowest such Reference Treasury Dealer Quotations, or (ii) if the Quotation Agent is given fewer than five such
Reference Treasury Dealer Quotations, the average of all such quotations, or (iii) if only one Reference Treasury Dealer Quotation is received, such quotation. 

“Quotation Agent” means the Reference Treasury Dealer appointed by the Company. 

“Reference Treasury Dealer” means each of BofA Securities, Inc., Morgan Stanley & Co. LLC and Wells Fargo Securities, LLC
(or their respective affiliates that are primary U.S. government securities dealers in New York City, each of which the Company refers to as a Primary Treasury Dealer) and their respective successors and two other nationally recognized investment
banking firms that are Primary Treasury Dealers appointed from time to time by the Company; provided, however, that if any of the foregoing shall cease to be a Primary Treasury Dealer, the Company will substitute therefor another Primary Treasury
Dealer. 
 “Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any redemption date,
the average, as determined by the Quotation Agent, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Quotation Agent by such Reference Treasury
Dealer at 5:00 p.m., New York City time, on the third business day preceding such redemption date. 
 “Treasury Rate” means,
with respect to any redemption date, the rate per annum equal to the semi-annual equivalent yield to maturity of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount)
equal to the Comparable Treasury Price for such redemption date. 
 All payments made by the Guarantor with respect to the Guarantee shall
be made free and clear of and without withholding or deduction for or on account of any present or future income, stamp or other tax, duty, levy, impost, assessment or other governmental charge of any nature whatsoever imposed or levied by or on
behalf of the government of the United Kingdom, of any territory of the United Kingdom or by any authority or agency therein or thereof having the power to tax (collectively, “Taxes”), unless the Guarantor is required to withhold or deduct
Taxes by law. 
 If an Event of Default with respect to the Securities of this series shall occur and be continuing, the principal amount of
and accrued and unpaid interest, if any, on the Securities of this series may be declared due and payable in the manner and with the effect provided in the Indenture. 

The Indenture contains provisions for defeasance at any time of the entire indebtedness of this Security or certain restrictive covenants and
Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth therein. 












 The Indenture permits, with certain exceptions as therein provided, the amendment thereof
and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Company and the Trustee with the consent of the Holders of a
majority in principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of specified percentages in principal amount of the Securities of each series at
the time Outstanding, on behalf of the Holders of all Securities of such series, to waive compliance by the Company with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent
or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof,
whether or not notation of such consent or waiver is made upon this Security. 
 No reference herein to the Indenture and no provision of
this Security or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or
currency, herein prescribed. 
 As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this
Security is registerable in the Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Company in any place where the principal of and any premium and interest on this Security are payable,
duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new
Securities of this series and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. 

The Securities of this series are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of
$1,000. As provided in the Indenture and subject to certain limitations therein set forth, Securities of this series are exchangeable for a like aggregate principal amount of Securities of this series and of like tenor of a different authorized
denomination, as requested by the Holder surrendering the same. 
 No service charge shall be made for any such registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith. 

Prior to due presentment of this Security for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary. 

Interest on this Security shall be computed on the basis of a 360-day year consisting of twelve 30-day months. 
 All terms used but not defined in this Security which are defined in the Indenture shall
have the meanings assigned to them in the Indenture. 
 This Security shall be governed by and construed in accordance with the laws of the
State of New York without giving effect to the conflict of laws provisions thereof. 












 ASSIGNMENT 

I or we assign and transfer this Security to: 
  

	
	  

(Insert assignee’s social security or tax I.D. number)

	
	  

(Print or type name, address and zip code of assignee)


 and irrevocably appoint: 
 as
agent to transfer this Security on the books of the Company. The agent may substitute another to act for him. 
  

							
	Date:	 		 	Your	 	
	         _______________________________________	 		 	Signature:	 	          

		 		 		 	(Sign exactly as your name appears on the face of this Security)

  

					
	Signature Guarantee:	 	          
	 	

 Signatures must be guaranteed by an “eligible guarantor institution” meeting the requirements of the
Security Registrar, which requirements include membership or participation in the Security Transfer Agent Medallion Program (“STAMP”) or such other “signature guarantee program” as may be determined by the Security Registrar in
addition to, or in substitution for, STAMP, all in accordance with the Securities Exchange Act of 1934, as amended. 












 NOTATION OF GUARANTEE 

For value received, the undersigned Guarantor (which term includes any successor Person under the Indenture), subject to the provisions in the Indenture and
the terms of the Securities of this series, has fully, unconditionally and irrevocably guaranteed to and for the benefit of each Holder and the Trustee the due and prompt payment in full of all amounts which may at any time be or become from time to
time due and payable by the Company under the Indenture or otherwise with respect to the Securities of this series registered in such Holder’s name, at their stated due dates or when otherwise due in accordance with the terms thereof. The
obligations of the Guarantor to the Holders of Securities and to the Trustee pursuant to the Guarantee under the Indenture are expressly set forth in Article Fifteen of the Indenture and reference is hereby made to the Indenture for the precise
terms of the Guarantee. Each Holder of a Security, by accepting the same, (a) agrees to and shall be bound by such provisions and (b) appoints the Trustee
attorney-in-fact of such Holder for the purpose of such provisions. 
  

			
	Aon plc
		
	By:	 	  

		 	Name: Paul Hagy
		 	Title: Senior Vice President and Treasurer