This is a list of how many students were named National Merit Semifinalists from Texas high schools. The press release has the names of the students and is widely available on the internet.
The Press Release lists the schools by the city where the school is located, which in Texas is confusing since school district boundaries don't match city limits. For example, Hebron High is located in the city of Carrollton, but is in the Lewisville ISD.
Source: Press Release dated 9-12-2018 from National Merit Scholarship Corporation
Number - School (City where the school is located, not necessarily the school district name)
75 - TX Academy Math/Science TAMS (Denton)
62 - Plano West (Plano)
57 - Westwood High (Austin)
39 - St. John's School (Houston)
35 - Plano East (Plano)
33 - Coppell (Coppell)
32 - Liberal Arts & Science Academy (Austin)
31 - St. Mark's School of Texas (Dallas)
29 - Clements (Sugar Land)
28 - Total Homeschoolers statewide
28 - Westlake (Austin)
27 - Highland Park (Dallas)
27 - The Woodlands College Park (The Woodlands)
24 - Seven Lakes (Katy)
22 - Flower Mound (Flower Mound)
21 - Carroll (Southlake)
21 - Clear Lake (Houston)
21 - Marcus (Flower Mound)
20 - Hockaday (Dallas)
18 - Liberty (Frisco)
17 - Colleyville Heritage (Colleyville)
17 - Dulles (Sugar Land)
15 - Dawson (Pearland)
14 - De Bakey Health Professions (Houston)
14 - Kinkaid School (Houston)
14 - Plano Senior (Plano)
14 - Vandergrift (Austin)
13 - Allen (Allen)
13 - Memorial (Houston)
13 - St. Stephen's Episcopal School (Austin)
13 - The Woodlands (The Woodlands)
12 - Bellaire (Bellaire)
12 - Carnegie Vanguard (Houston)
12 - Hebron (Carrollton)
12 - Independence (Frisco)
12 - St. Mary's Hall (San Antonio)
11 - Paschal (Fort Worth)
11 - Tompkins (Katy)
9 - Greenhill School (Addison)
9 - McNeil (Austin)
9 - Round Rock (Round Rock)
9 - Strake Jesuit (Houston)
9 - Talented & Gifted TAG magnet (Dallas)
8 - Keller (Keller)
8 - Reedy (Frisco)
7 - Keystone School (San Antonio)
7 - Kingwood (Kingwood)
7 - Klein Oak (Spring)
7 - Lubbock (Lubbock)
7 - Taylor (Katy)
7 - Ursuline Academy (Dallas)
6 - A&M Consolidated (College Station)
6 - Anderson (Austin)
6 - Basis SA Shavano Campus (San Antonio)
6 - Clear Springs (League City)
6 - Heritage (Frisco)
6 - High School Performing/Visual Arts (Houston)
6 - Wakeland (Frisco)
5 - Cinco Ranch (Katy)
5 - College Station (College Station)
5 - Cooper (The Woodlands)
5 - Friendswood (Friendswood)
5 - Frisco (Frisco)
5 - Garland (Garland)
5 - Grapevine (Grapevine)
5 - JJ Pearce (Richardson)
5 - St. Agnes Academy (Houston)
5 - St. Andrews Episcopal School (Austin)
5 - Vista Ridge (Cedar Park)
4 - Central (Keller)
4 - Clark (San Antonio)
4 - Jesuit (Dallas)
4 - Klein (Klein)
4 - Lake Travis (Austin)
4 - Lovejoy (Lucas)
4 - Martin (Arlington)
4 - Northside Health Careers (San Antonio)
4 - Science Academy of South Texas (Mercedes)
4 - St. Dominic Savio Catholic (Austin)
4 - Tomball Memorial (Tomball)
4 - Trinity Valley School (Fort Worth)
3 - Atascocita (Humble)
3 - Awty International (Houston)
3 - Cedar Park (Cedar Park)
3 - Centennial (Frisco)
3 - Cistercian Prep (Irving)
3 - Clear Falls (League City)
3 - Collegiate Academy (Hurst)
3 - Cy-Fair (Cypress)
3 - Elkins (Missouri City)
3 - Episcopal School of Dallas (Dallas)
3 - Lamar (Houston)
3 - Langham Creek (Houston)
3 - Lewisville (Lewisville)
3 - Live Oak Classical (Waco)
3 - Midway (Waco)
3 - North Hills Prep (Irving)
3 - Pflugerville (Pflugerville)
3 - Reagan (San Antonio)
3 - Regents (Austin)
3 - Richardson (Richardson)
3 - RL Turner (Carrollton)
3 - Rockwell-Heath (Heath)
3 - Roosevelt (San Antonio)
3 - Science & Engineering SEM magnet (Dallas)
3 - Stephen F. Austin (Sugar Land)
3 - Stratford (Houston)
3 - Trinity Christian Academy (Addison)
3 - Village School (Houston)
3 - West Brook (Beaumont)
2 - Birdville (North Richland Hills)
2 - Boerne (Boerne)
2 - Boerne Champion (Boerne)
2 - Booker T Performing/Visual Arts magnet (Dallas)
2 - Brandeis (San Antonio)
2 - Byron Nelson (Trophy Club)
2 - Christian Life Prep (Fort Worth)
2 - Clear Brook (Friendswood)
2 - Clear Creek (League City)
2 - Coram Deo Academy (Flower Mound)
2 - Cornerstone Christian (McKinney)
2 - Covenant Christian (Colleyville)
2 - Cypress Creek (Houston)
2 - Cypress Falls (Houston)
2 - Cypress Ranch (Cypress)
2 - Cypress Woods (Cypress)
2 - Dubiski (Grand Prairie)
2 - Guyer (Denton)
2 - Incarnate Word Academy (Corpus Christi)
2 - Islamic School (Irving)
2 - Jersey Village (Houston)
2 - Lady Bird Johnson (San Antonio)
2 - Lakeview Centennial (Garland)
2 - LD Bell (Hurst)
2 - Lone Star (Frisco)
2 - Lucas Christian Academy (Lucas)
2 - McCallum (Austin)
2 - McKinney (McKinney)
2 - McKinney North (McKinney)
2 - Meridian World (Round Rock)
2 - Newman Smith (Carrollton)
2 - Oakridge School (Arlington)
2 - Prestonwood Christian (Plano)
2 - Richland (North Richland Hills)
2 - San Marcos (San Marcos)
2 - Tivy (Kerrville)
2 - Trinity (Euless)
2 - Waxahachie Global (Waxahachie)
2 - Westlake Academy (Westlake)
2 - Wylie East (Wylie)
1 - Abilene High School (Abilene)
1 - Academy of Technology, Eng, Math, Science (Abilene)
1 - Akins (Austin)
1 - Aledo (Aledo)
1 - Allen Academy (Bryan)
1 - All Saints Episcopal (Fort Worth)
1 - Amarillo (Amarillo)
1 - Argyle (Argyle)
1 - Arlington (Arlington)
1 - Ascension Academy (Amarillo)
1 - Austin Peace Academy (Austin)
1 - Austin Tennis Academy College Prep (Austin)
1 - Ball (Galveston)
1 - Bellville (Bellville)
1 - Benbrook (Benbrook)
1 - Bethesda Christian (Fort Worth)
1 - Bishop Gorman (Tyler)
1 - Boyd (McKinney)
1 - Brazoswood (Clute)
1 - British International (Katy)
1 - Carrizo Springs (Carrizo Springs)
1 - Cathedral (El Paso)
1 - Christian Heritage Classical (Longview)
1 - Clemens (Schertz)
1 - Concordia (Round Rock)
1 - Coronado (El Paso)
1 - Cypress Lakes (Katy)
1 - Dripping Springs (Dripping Springs)
1 - East View (Georgetown)
1 - Eaton (Haslet)
1 - El Paso (El Paso)
1 - Franklin (El Paso)
1 - Ft. Worth Christian (North Richland Hills)
1 - Gainsville (Gainsville)
1 - Geneva School (Boerne)
1 - Granbury (Granbury)
1 - Harmony School of Advancement (Houston)
1 - Harmony School of Innovation (Sugar Land)
1 - Harmony Science Academy (Euless)
1 - Hays (Buda)
1 - Hill Country Christian (Austin)
1 - Houston Academy International Studies (Houston)
1 - Imagine International (McKinney)
1 - Incarnate Word (Houston)
1 - Ingram (Ingram)
1 - Inter'l Leadership at Saginaw (Fort Worth)
1 - Iraan (Iraan)
1 - Irving (Irving)
1 - iSchool High at University Park (Houston)
1 - iUniversity Prep (Grapevine)
1 - Judson Early College (Live Oak)
1 - Katy (Katy)
1 - La Feria (La Feria)
1 - Lakehill Prep (Dallas)
1 - Lampasas (Lampasas)
1 - La Vernia (La Vernia)
1 - Liberty Christian School (Argyle)
1 - Llano (Llano)
1 - Longview (Longview)
1 - MacArthur (Irving)
1 - Magnolia (Magnolia)
1 - Mansfield Legacy (Mansfield)
1 - Manvel (Manvel)
1 - Montgomery (Montgomery)
1 - New Heights Christian (Houston)
1 - Nolan Catholic (Fort Worth)
1 - Our Lady of the Hills (Kerrville)
1 - Parish Episcopal (Dallas)
1 - Pearland (Pearland)
1 - Pope John Paul (Plano)
1 - Ranch (Richmond)
1 - Ray (Corpus Christi)
1 - Rider (Wichita Falls)
1 - Robert E. Lee (Tyler)
1 - Rowe (McAllen)
1 - Rowlett (Rowlett)
1 - Sachse (Sachse)
1 - Saginaw (Saginaw)
1 - School of Science & Tech (San Antonio)
1 - Second Baptist School (Houston)
1 - Seguin (Seguin)
1 - Shadow Creek (Pearland)
1 - Sharpstown International (Houston)
1 - Shelton School (Dallas)
1 - Smithson Valley (Spring Branch)
1 - South Texas Academy Medical (Olmito)
1 - Stephen F. Austin (Austin)
1 - St. John XXIII (Katy)
1 - St. Joseph (Victoria)
1 - St. Michael's Catholic (Austin)
1 - St. Paul (Shiner)
1 - Tarrant County College South (Fort Worth)
1 - Texas (Texarkana)
1 - The Colony (The Colony)
1 - Tomball (Tomball)
1 - Travis (Richmond)
1 - UME Prep Academy (Dallas)
1 - Vanguard College Prep (Waco)
1 - Veritas Academy (Austin)
1 - Westchester Academy (Houston)
1 - Westside (Houston)
1 - Wichita Falls (Wichita Falls)
1 - Wimberley (Wimberley)
1 - Yavneh Academy (Dallas)
Homeschoolers by City
1 - Anna
1 - Boerne
1 - Coppell
1 - Dallas
1 - Garland
1 - Grand Prairie
1 - Howe
1 - Parker
1 - Plano
1 - Tyler
1 - Wylie
2 - Canton
2 - Ft. Worth
2 - McKinney
2 - Sugar Land
4 - Houston
5 - Austin