Estate of O'Neill

2026 S.D. 1
CourtSouth Dakota Supreme Court
DecidedJanuary 7, 2026
Docket30969
StatusPublished

This text of 2026 S.D. 1 (Estate of O'Neill) is published on Counsel Stack Legal Research, covering South Dakota Supreme Court primary law. Counsel Stack provides free access to over 12 million legal documents including statutes, case law, regulations, and constitutions.

Bluebook
Estate of O'Neill, 2026 S.D. 1 (S.D. 2026).

Opinion

#30969-r-MES 2026 S.D. 1

IN THE SUPREME COURT OF THE STATE OF SOUTH DAKOTA

****

IN THE MATTER OF THE ESTATE OF JUDITH ANN O’NEILL, Deceased.

APPEAL FROM THE CIRCUIT COURT OF THE SIXTH JUDICIAL CIRCUIT TODD COUNTY, SOUTH DAKOTA

THE HONORABLE BOBBI J. RANK Judge

MICHAEL V. WHEELER of DeMersseman Jensen Tellinghuisen & Huffman, LLP Rapid City, South Dakota

JAMES G. SWORD Hot Springs, South Dakota Attorneys for appellant James Anthony O’Neill.

CLINT SARGENT of Meierhenry Sargent LLP Sioux Falls, South Dakota

JAMES S. SIMKO of Cadwell, Sanford, Deibert & Garry LLP Sioux Falls, South Dakota Attorneys for appellees Sandy Lang, Beth O’Neill, and Richard O’Neill.

CONSIDERED ON BRIEFS OCTOBER 7, 2025 OPINION FILED 01/07/26 #30969

SALTER, Justice

[¶1.] James Anthony O’Neill (Tony), filed a petition for formal probate of his

mother’s last will and testament and a first codicil (collectively the Will) which left

her entire estate to Tony and specifically disinherited her other children. Tony’s

siblings filed an objection, asserting the Will was the product of undue influence. At

the trial of this undue influence claim, the circuit court relied upon the doctrine of

collateral estoppel to admit findings of fact and conclusions of law entered in a prior

civil case involving Tony and his brother, Richard O’Neill (Rick). The court also

instructed the jury that all of the previous findings and conclusions—including

adverse credibility determinations regarding Tony’s testimony—had been

conclusively established. The jury determined that Tony unduly influenced his

mother, and as a result, the Will was invalid. Tony appeals. We reverse and

remand for a new trial.

Factual and Procedural Background

[¶2.] Judith and Dean O’Neill were a married couple who farmed and

ranched in Bennett County and raised their four children, Tony, Rick, Sandy Lang,

and Beth O’Neill. When Tony and Rick became adults, they began their own

farming and ranching operation in the area, and the two brothers worked together

for a number of years.

[¶3.] But beginning in 2011, Tony and Rick began to separate their business

interests and their related real and personal property. As part of the effort, they

attempted to divide their property through written agreements. Eventually,

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however, there was a significant amount of conflict as to the effect and

enforceability of the agreements.

[¶4.] In order to resolve their differences and complete the division of the

two brothers’ property, Tony sought judicial intervention and commenced a civil

action in Bennett County (the prior action). The prior action was tried to the court

in July 2013, and, simply put, Tony lost badly on all issues. The court enforced both

a land separation agreement and an asset separation agreement and divided the

remaining assets in a way that resulted in Rick receiving more property than Tony,

in part, Rick later explained, because Tony had drafted the agreements unwisely.

[¶5.] The court in the prior action entered comprehensive written findings of

fact and conclusions of law related to the brothers’ business dealings and property.

Among these were discrete findings and conclusions about the land separation

agreement, including allegations that Rick forged Tony’s signature and claims that

Tony surreptitiously listed the brothers’ farm and cattle businesses as collateral on

loans for Tony’s own separate ventures.

[¶6.] In connection with its resolution of these issues contrary to Tony’s

positions, the prior court made multiple adverse credibility determinations in which

it found Tony’s version of particular facts relating to his dealings with Rick or their

farming and ranching business were “not credible.” In addition, the prior court

made other findings concerning Tony’s conduct vis-à-vis Rick that were highly

unfavorable, including the following pointed critique:

Tony’s strategy in dealing with Rick has been one of dishonesty and malicious mischief. Tony was not honest with Rick before this lawsuit, and during this lawsuit, in the handling of the corporate financing. In addition, Tony committed fraud on this

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court by lying about the existence of a signed Land Separation Agreement. . . . Tony was also not honest with this court when he denied the existence of the negotiated agreement reached between the parties.1

[¶7.] Seemingly unrelated to her sons’ business dispute, Judith had grown

weary of Dean’s mistreatment, which she stated included years of verbal and

physical abuse. In 2013, she moved from the family’s farm to Rapid City, and she

commenced a divorce action in 2014. During the pendency of the divorce, Judith

executed her Will on August 26, 2016, leaving to Tony 100% of her interest in all

the real estate she and Dean owned. Judith also stated in her Will, “It is my

specific request that Tony receive the family ranch home place upon my death.”

She left the remainder of her estate to Tony and her daughter Sandy, in equal

shares.

[¶8.] As explained by her former divorce lawyers during their testimony in

the undue influence trial, Judith’s effort to obtain a divorce was protracted. She

believed the reason was, at least in part, attributable to delay tactics orchestrated

by Dean. As time went by, Judith also attributed some of the blame to Sandy, who

sought a conservatorship for Judith only days before the scheduled divorce trial.

Judith and Dean ultimately settled their divorce in April 2018, and the resulting

decree required Dean to make an equalization payment to Judith in the amount of

$605,000.

1. Tony appealed the judgment in the prior action, and we affirmed it in a published decision, with the exception of a punitive damage award imposed against Tony, which we vacated. See O’Neill v. O’Neill, 2016 S.D. 15, 876 N.W.2d 486.

-3- #30969

[¶9.] Prior to this, though, Judith executed the first codicil to the Will on

July 26, 2017, which removed Sandy from her estate plan. Under the first codicil,

Judith left all her real estate, as well as the entirety of the remainder of her estate,

to Tony and excluded her other children by stating, “As it relates to Richard O’Neill,

Beth O’Neill, and Sandy Lang f/n/a [sic] Sandy O’Neill, they are specifically and

intentionally omitted form [sic] this Will and shall not receive anything from my

Estate.”

[¶10.] Judith died on November 28, 2018, and Tony filed a petition for formal

probate of the Will on March 20, 2019. His siblings—Rick, Sandy, and Beth (the

Respondents)—filed an objection, alleging that Judith’s Will was the product of

undue influence, lack of capacity, fraud, duress, mistake, and revocation.

[¶11.] Prior to the undue influence trial, the Respondents moved for an order

declaring the factual findings from the prior action as conclusively established

pursuant to the doctrine of collateral estoppel. In their written submissions to the

circuit court, the Respondents described the prior action as “a tense, lengthy, and

deeply personal case that centered on document validity (partnership separation

agreements and land separation agreements) and fiduciary duties owed to the

brothers’ farm corporations.”

[¶12.] The Respondents alleged a relationship between the outcome of the

prior litigation involving business issues between Tony and Rick and the undue

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Cite This Page — Counsel Stack

Bluebook (online)
2026 S.D. 1, Counsel Stack Legal Research, https://law.counselstack.com/opinion/estate-of-oneill-sd-2026.