The City of Houston lies in three counties: Harris (583.450 sq.mi.), Fort Bend (8.080 sq.mi.), and Montgomery (2.598 sq.mi.). Harris County contains part or all of 35 incorporated areas.
Under Texas’ Municipal Annexation Act of 1963, cities have certain powers over surrounding unincorporated areas, termed the Extraterritorial Jurisdiction. ETJ is a function of population; for cities over 100,000, it can cover all unincorporated area within five miles of any point on the city limits. Houston’s ETJ encompasses 1,311.950 sq.mi., excluding the area of cities that lie within it.
TOPOGRAPHY: Houston lies largely in the northern portion of the Gulf coastal plain, a 40- to 50-mile-wide swath along the Texas Gulf Coast. Typically, elevation rises approximately one foot per mile inland.