Ontario vs. U.S. Cohabitation Agreements – Key Differences for Cross-Border Couples

Why Cross-Border Couples Need to Understand Cohabitation Agreements

A cohabitation agreement in Ontario is a legally binding contract between common-law partners that sets out each person’s rights and obligations regarding property, support, and other matters if the relationship ends. However, what may be valid and enforceable in Ontario does not necessarily hold the same weight in U.S. states, where family law is governed by a patchwork of state-specific rules.

For cross-border couples, this distinction is critical. Without careful planning, one partner may discover that terms negotiated and agreed upon in Ontario are not enforceable south of the border. For example, Ontario law requires full financial disclosure and often recommends independent legal advice (ILA) for both parties to ensure enforceability. In contrast, certain U.S. states may not impose the same disclosure obligations, but may allow challenges based on fairness or unconscionability at the time of enforcement.

The risk lies in assuming that a cohabitation agreement will automatically apply equally in both jurisdictions. In reality, cross-border couples must recognize that Ontario’s Family Law Act and U.S. state laws take very different approaches. Property division, spousal support rights, and even recognition of common-law partnerships may vary widely.

Legal Framework in Ontario

In Ontario, cohabitation agreements are governed by the Family Law Act, which provides the legal foundation for couples who are not married but wish to formalize their rights and responsibilities. These agreements are commonly used by common-law partners to outline how property, support, and financial matters will be handled if the relationship ends.

To be valid and enforceable in Ontario, a cohabitation agreement must meet specific requirements:

• Written Form – Verbal agreements carry little to no weight under Ontario law. A cohabitation agreement must be in writing and signed by both partners.
• Full Financial Disclosure – Each partner must provide complete and honest disclosure of income, assets, debts, and liabilities. Without this, the agreement may be challenged later as unfair or incomplete.
• Independent Legal Advice (ILA) – While not strictly mandatory, ILA is strongly recommended and often critical to enforceability. Courts may set aside agreements if one partner claims they did not understand their rights or were pressured to sign without legal guidance.

It is also important to recognize the limits of cohabitation agreements in Ontario. Couples cannot use these agreements to predetermine issues relating to child custody or child support. These matters are always subject to the best interests of the child standard under the Children’s Law Reform Act and the Divorce Act, and no private contract can override that principle.

Legal Framework in the United States

Unlike Ontario, which has a single provincial statute that governs cohabitation agreements, the United States has no federal law that regulates them. Instead, the rules vary significantly from one state to another, creating a patchwork of approaches that can be confusing for cross-border couples.

In some states—such as California, New York, and Washington—cohabitation agreements are recognized and enforceable, provided they are drafted in writing and meet basic contract law requirements. These agreements often address property ownership, financial responsibilities, and support obligations. However, the extent of recognition and the weight given to such agreements differ widely.

Other states may be more restrictive. For example, jurisdictions that historically rejected “common-law marriage” may also limit the enforceability of agreements between unmarried partners. In these states, courts may view cohabitation contracts with scepticism, especially if they appear to conflict with public policy or resemble agreements based solely on a domestic or intimate relationship.

Enforceability in the U.S. typically relies on general contract principles. Courts will examine whether:

• Both parties entered into the agreement voluntarily.
• There was consideration (something of value exchanged, such as promises about property or financial support).
• The agreement complies with public policy in that state.

As in Ontario, courts in the U.S. will generally not allow agreements to dictate matters such as child custody or child support, since these issues are considered matters of public interest and are determined by the courts based on the best interests of the child.

For couples with ties to both Ontario and the United States, this variability creates uncertainty. A cohabitation agreement valid in Ontario may not be automatically enforceable in a U.S. state where the couple later resides or holds property. As a result, it is often necessary for cross-border partners to seek legal advice in both jurisdictions to ensure their agreement will be respected on both sides of the border.

Key Differences Between Ontario and U.S. Agreements

For couples navigating a cross-border relationship, understanding the practical differences between Ontario cohabitation agreements and their U.S. counterparts is essential. While both jurisdictions allow partners to make private arrangements, the scope and reliability of these agreements differ considerably.

Recognition and Enforceability

In Ontario, cohabitation agreements are recognized under the Family Law Act and carry significant legal weight, provided the agreement is in writing, supported by full financial disclosure, and ideally backed by independent legal advice. Courts in Ontario generally uphold these agreements unless they are found to be unconscionable or improperly executed.

In the United States, there is no uniform legal standard. Recognition depends entirely on the state where the agreement is enforced. Some states embrace these contracts as valid, while others impose strict limits—or may not recognize them at all. This creates uncertainty for couples who split their time between Ontario and different U.S. jurisdictions.

Property Division

Ontario agreements allow couples to clearly set out how property will be divided if the relationship ends. This includes ownership of the matrimonial home, personal property, and investments, subject to disclosure and fairness requirements. Courts usually respect these clauses unless there is evidence of undue pressure or incomplete disclosure.

In the U.S., property division outcomes may differ widely by state. Some states will enforce property-sharing provisions under contract law, while others may refuse to uphold arrangements that resemble community property rules or that conflict with local statutes.

Spousal Support

Ontario courts will generally uphold spousal support provisions in a cohabitation agreement but retain discretion to review them for fairness at the time of enforcement. If a clause would cause serious financial hardship to one partner, a judge may intervene and adjust the terms.

In the U.S., enforcement again varies. Certain states will enforce spousal support clauses as written, while others give judges broad discretion to modify or disregard them if they are deemed unfair or against public policy.

Child-Related Provisions

In both Ontario and the United States, private agreements cannot predetermine child custody or child support. These matters remain under the authority of the courts and must be decided based on the best interests of the child. The difference lies in how each jurisdiction treats such clauses: Ontario courts typically strike them down as unenforceable, while some U.S. states may simply disregard them without invalidating the rest of the agreement.

Cross-Border Challenges Couples Face

For couples with ties to both Ontario and the United States, the question of which jurisdiction’s law applies can be one of the most significant challenges. If partners live primarily in Ontario, Ontario law will usually govern their cohabitation agreement. However, if they later move to or acquire property in the U.S., local state law may come into play. This creates uncertainty, since an agreement valid in Ontario may not automatically be enforceable south of the border.

Another key difficulty is recognition of agreements if challenged in the other country. For example, an Ontario court may enforce a cohabitation agreement in line with the Family Law Act, but if one partner later seeks enforcement in a U.S. state, the court there may apply different contract principles or public policy tests. In states that are less receptive to cohabitation contracts, the agreement may be rejected altogether. This can leave couples vulnerable to costly disputes and inconsistent outcomes.

Cross-border couples must also navigate estate planning complications. When assets such as real estate, investments, or retirement accounts exist in both Ontario and the United States, different inheritance and probate laws apply. An Ontario cohabitation agreement may clarify how property is to be divided between partners, but U.S. estate law may not recognize those same provisions. Without careful coordination, this can create conflicts between surviving partners and family members, particularly in blended families or situations involving adult children.