The Burlington and Missouri River Railroad Company v. Mills County, Iowa was a case heard by the United States Supreme Court in 1869. The case centered around the question of whether the railroad company had the right to build a bridge across the Missouri River in Mills County, Iowa. The railroad company argued that it had the right to build the bridge under the Commerce Clause of the United States Constitution, which gives Congress the power to regulate interstate commerce. The county argued that the bridge would be a public nuisance and that the railroad company did not have the right to build it without the county's permission. The Supreme Court ultimately sided with the railroad company, ruling that the Commerce Clause gave the railroad company the right to build the bridge. The Court reasoned that the bridge was necessary for the efficient transportation of goods and people across state lines, and that the county's concerns about public nuisance were outweighed by the public benefit of the bridge. The Court also noted that the bridge would be subject to state and federal regulations, and that the county had no authority to prevent its construction. The ruling established the principle that the Commerce Clause gives the federal government the power to regulate interstate commerce, and that states cannot interfere with this power.

In the case of The Burlington and Missouri River R.R. Company v. Mills County, Iowa, Chief Justice Chase delivered a dissenting opinion in which he argued that the state legislature had no authority to grant tax exemptions for railroad companies as it was not within their power to do so under the Constitution of Iowa or any other law passed by Congress. He further argued that such an exemption would be unconstitutional because it would give preferential treatment to one class over another and thus violate both due process and equal protection clauses of the Fourteenth Amendment. In addition, he noted that if this kind of exemption were allowed then all states could pass similar laws granting special privileges to certain classes at the expense of others; something which should not be permitted under our system of government based on equality before the law for all citizens regardless of race or economic status.