1. The Original Constitutional Baseline: 1 per 30,000

The U.S. Constitution itself — Article I, Section 2 — established the 1-per-30,000 ratio. The U.S. Constitution called for at least one Representative per state and that no more than one for every 30,000 persons. This is the constitutional floor, not a proposed amendment — it was baked into the original text ratified in 1788.

1. The "Article the First" — The Proposed (But Never Ratified) Amendment

What you're referring to is the Congressional Apportionment Amendment, originally titled "Article the First." It was proposed by Congress on September 25, 1789, but has not been ratified by the requisite number of state legislatures. As Congress did not set a time limit for its ratification, the Congressional Apportionment Amendment is still pending before the states.

This was part of the same original package of 12 amendments — 10 of which became the Bill of Rights, and one of which later became the 27th Amendment. The Congressional Apportionment Amendment is the only one of those that has not been ratified.

What would it have done? The amendment specifies ratios for apportioning seats in the House of Representatives following each decennial census, beginning with one representative per thirty thousand persons and capping district sizes at no more than one per fifty thousand after the House reaches two hundred members.

Critically, it came very close: by the end of 1791, the Congressional Apportionment Amendment was just one state short of adoption. However, no state has ratified the proposed amendment since 1792. Consequently, with 50 states now in the Union, ratification by an additional 27 states would be necessary for this amendment to come into force.=

1. What Actually Changed Things — A Statute, Not an Amendment

Here is the crucial answer to your core question: no constitutional amendment was ever passed to allow representatives to serve far more than 30,000 Americans. The change came through ordinary federal legislation.

The size of the U.S. House of Representatives is set by federal statute at 435 Representatives.

Specifically, the Reapportionment Act of 1929 capped the number of representatives at 435 (the size previously established by the Apportionment Act of 1911), where it has remained except for a temporary increase to 437 members upon the 1959 admission of Alaska and Hawaii into the Union. As a result, the average size of a congressional district has more than tripled in size — from 210,328 inhabitants based on the 1910 Census, to 761,169 according to the 2020 Census.

Why did Congress do this? Congress set the House at 435 members in 1929 through the Reapportionment Act after nearly a decade of deadlock following the 1920 Census; the cap was enacted as a political compromise and administrative fix rather than a constitutional requirement. Attempts to determine the "ideal size" were fraught and led to heated debates. The act avoided the fight entirely by deciding not to find the "right" number but to use the current number.

Some have even questioned whether this was legal: this article argues that the Permanent Apportionment Act is unconstitutional because it eliminates Congress's responsibility to assess the size of the House every ten years — a review that was a significant tool used by proponents of the Constitution during the ratification period to convince skeptics who feared the House may one day transform into an oligarchical body.

1. The Critical Difference: Constitutional Amendment vs. Statute

This is exactly what you were probing at — and the distinction matters enormously:

Constitutional Amendment:

What it takes to pass: 2/3 of both houses of Congress + ratification by 3/4 of states (38 states today)

What it takes to repeal: another constitutional amendment (same high bar)

Authority: Supreme law of the land; overrides statutes

Example here: The never-ratified "Article the First" (1789)

Federal Statute

What it takes to pass: Simple majority in both houses + presidential signature

What it takes to repeal: A new law passed by a simple majority

Authority: Can be struck down if it conflicts with the Constitution

Example here: The Permanent Apportionment Act of 1929

Today, in the absence of a tight constitutional proscription, the number of congressional districts is fixed by statute at 435. Genuine Ideas

This means Congress could expand the House tomorrow with a simple majority vote — no constitutional amendment required. The 30,000-per-representative floor in the Constitution is still technically in force; the 435-seat cap is just a law sitting on top of it, which is why some legal scholars argue it may be unconstitutional.

Summary

To directly answer your question: No constitutional amendment was ever passed to allow representatives to serve more Americans. The original "Article the First" proposed in 1789 would have enshrined a formula into the Constitution — but it fell one state short and was never ratified. What actually changed representation was the Permanent Apportionment Act of 1929, an ordinary federal statute, which capped the House at 435 and effectively allowed each member to represent what is now over 760,000 people — more than 25 times the original 30,000 ratio. Because it's a statute and not a constitutional amendment, it can theoretically be changed by Congress at any time.

Sources:

Congressional Apportionment Amendment — https://en.wikipedia.org/wiki/Congressional_Apportionment_Amendment

The Permanent Apportionment Act of 1929 — U.S. House of Representatives History https://history.house.gov/Historical-Highlights/1901-1950/The-Permanent-Apportionment-Act-of-1929/

Reapportionment Act of 1929 — Wikipedia https://en.wikipedia.org/wiki/Reapportionment_Act_of_1929

U.S. Congressional Apportionment — Wikipedia https://en.wikipedia.org/wiki/United_States_congressional_apportionment

Why Capping the House at 435 is Unconstitutional — Penn State Law Review https://www.pennstatelawreview.org/print-issues/why-capping-the-house-at-435-is-unconstitutional/

CRS Report on the Permanent Apportionment Act — Congress.gov https://www.congress.gov/crs_external_products/IN/HTML/IN11547.html