ORDER TO SHOW CAUSE

PHILIP A. BRIMMER, District Judge.

The Court takes up this matter sua sponte on Defendant's Notice of Removal [Docket No. 1]. Defendant states that the Court has subject matter jurisdiction over this lawsuit pursuant to 28 U.S.C. § 1332(a). Docket No. 1 at 2-3, ¶¶ 2-5.

In every case and at every stage of the proceeding, a federal court must satisfy itself as to its own jurisdiction, even if doing so requires sua sponte action. See Citizens Concerned for Separation of Church & State v. City & County of Denver, 628 F.2d 1289, 1297 (10th Cir. 1980). Absent an assurance that jurisdiction ex ists, a court may not proceed in a case. See Cunningham v. BHP Petroleum Great Britain PLC, 427 F.3d 1238, 1245 (10th Cir. 2005). Courts are well-advised to raise the issue of jurisdiction on their own, regardless of parties' apparent acquiescence. First, it is the Court's duty to do so. Tuck v. United Servs. Auto. Ass'n, 859 F.2d 842, 844 (10th Cir. 1988). Second, regarding subject matter jurisdiction, "the consent of the parties is irrelevant, principles of estoppel do not apply, and a party does not waive the requirement by failing to challenge jurisdiction." Ins. Corp. of Ireland v. Compagnie des Bauxites de Guinee, 456 U.S. 694, 702 (1982) (internal citations omitted). Finally, delay in addressing the issue only compounds the problem if, despite much time and expense having been dedicated to the case, a lack of jurisdiction causes it to be dismissed. See U.S. Fire Ins. Co. v. Pinkard Constr. Co., No. 09-cv-00491-PAB-MJW, 2009 WL 2338116, at *3 (D. Colo. July 28, 2009).

"The party invoking federal jurisdiction bears the burden of establishing such jurisdiction as a threshold matter." Radil v. Sanborn W. Camps, Inc., 384 F.3d 1220, 1224 (10th Cir. 2004). Defendant asserts that this Court has diversity jurisdiction under 28 U.S.C. § 1332(a). Pursuant to that section, "district courts shall have original jurisdiction of all civil actions where the matter in controversy exceeds the sum or value of $75,000, exclusive of interest and costs, and is between . . . citizens of different States." 28 U.S.C. § 1332(a).

Defendant states that plaintiff is a citizen of Colorado. Docket No. 1 at 2, ¶ 3. However, the evidence upon which defendant relies to establish plaintiff's citizenship — plaintiff's statement that he, "at all relevant times[,] resided in the State of Colorado, Docket No. 1-2 at 1, ¶ 1 — only addresses the issue of residency. Domicile, not residency or mailing address, is determinative of citizenship. Whitelock v. Leatherman, 460 F.2d 507, 514 (10th Cir. 1972) ("[A]llegations of mere `residence' may not be equated with `citizenship' for the purposes of establishing diversity."); see also Mississippi Band of Choctaw Indians v. Holyfield, 490 U.S. 30, 48 (1989) ("`Domicile' is not necessarily synonymous with `residence,' and one can reside in one place but be domiciled in another." (citations omitted)).

Because the defendant's allegations are presently insufficient to allow the Court to determine plaintiff's citizenship or whether the Court has jurisdiction, see United States ex rel. General Rock & Sand Corp. v. Chuska Dev. Corp., 55 F.3d 1491, 1495 (10th Cir. 1995) ("The party seeking the exercise of jurisdiction in his favor must allege in his pleading the facts essential to show jurisdiction.") (citations and internal quotation marks omitted), it is

ORDERED that, on or before 5:00 p.m. on December 5, 2018, defendant shall show cause why this case should not be remanded to state court due to the Court's lack of subject matter jurisdiction.