The rule is settled that, to give this court jurisdiction of a writ of error to a state court, it must appear affirmatively, not only that a federal question was presented for decision by the highest court of the state having jurisdiction, but that its decision was necessary to the determination of the cause, and that it was actually decided, or that the judgment as rendered could not have been given without deciding it. De Saussure v. Gaillard, 127 U.S. 216, 8 Sup. Ct. Rep. 1053; Johnson v. Risk, 137 U.S. 300, ante, 111. Tested by this rule, this writ of error cannot be sustained. The supreme court of Illinois held that title passed to that state by the act of congress, and that the plaintiff established a prima facie right to recover; but that as the state, in granting the lands to the countics, had the undoubted power to provide that purchasers who had bought and paid for the lands should be protected in their several purchases, and had so provided by its act of 1852, and this land had been 'sold by the United States' to Egan after September 28, 1850, within the meaning of that act, no title passed to the county. The judgment of the state court proceeded wholly upon the construction of the terms and conditions of the grant of the state to the county by the act of 1852, and as amended by the act of 1854, and the validity of those enactments was not drawn in question. The effect claimed by counsel as attributable to the act of congress of 1850, as operating as a grant in praesenti to the state of Illinois, was given to it by the supreme court, and the confirmatory act of congress of March 3, 1857, did not enter into the decision of the case, because under the conclusion reached there was no title in plaintiff to be confirmed. There was no decision against a claim or title asserted under the United States, but simply that the county did not obtain title under the grant of the state; that the act of 1852 imposed a positive duty on the county to transfer such title as it acquired to the purchaser from the United States; and that, where lands had been bought in good faith from the United States, the title to such lands did not become vested in the county, but passed to the purchaser under his entry. This construction by the state court of the laws of the state is controlling in the premises. gormley v. Clark, 134 U.S. 338, 348, 10 Sup. Ct. Rep. 554, and cases cited. It is said that as Cook county was under township organization law in 1852, and hence under the government of a board of supervisors, and not of county courts, it had no special legislative authority to dispose of swamp lands until the passage of the act of March 4, 1854, (Sess. Laws 1854, p. 184,) imparting that power, and that therefore the second section of the act of 1852 did not apply to that county. While this point does not seem to have been presented to the state court, yet, if the state did not intend to transfer title to the lands that had been entered from the United States, as was held by the court, the mere want of power to convey, which was at the next session of the general assembly supplied, would not require a different construction to the contrary of such intention. As the acts of congress referred to in the first and second errors assigned did not purport to vest title to swamp lands in Cook or any other county, and the court only passed upon the alleged grant by the state, we are unable to perceive that any federal question was, in this regard, necessarily or in fact decided.