Below, Thorton HS is 7th all time for regular season 4 x 800 (converted time from 2-mile relay), and Lyons HS is 8th, suggesting a couple of other teams in that relay are also still top-10.
If New Balance Nationals Outdoor existed in the 3rd week of June back when that relay was run, because Northern IL runners typically have 4-6 weeks of good track weather prior to their state meet, it is sensible the top teams in that relay could have improved by an average of 1 second per person for each team during the time from the IL state meet to the 3rd week of June.
That would move those top teams back into the top 5, or top 10 all-time. York HS had two times faster ('85 and '00), but those of those were run prior to their state meet, and were not subject to running prelims and then the next day finals, so their improvement might be measured from what they did in the state meet (absent injuries).
So...why is it true that those teams are still among the best ever for the relay?
Is it lack of 4 x 800m relays in other states' HS competitions?
Top 25 All-Time Boys High School 4 x 800
[post-season times, except those with an *]
7:28.75 Poly, Long Beach, Ca
NB Natls(R_) 6/17/11 Greensboro, NC
7:30.31n Charlotte, Punta Gorda, Fl
NB Natls(2) 6/17/11 Greensboro, NC
7:30.67 * Albemarle, Charlottesville, Va
Penn Relays-hs 4/25/09 Philadelphia, Pa
7:31.60n * Morris Hills, Rockaway, NJ
Penn Relays-hs(2) 4/25/09 Philadelphia, Pa
7:31.62 Northport, NY
NB Natls(R3) 6/16/18 Greensboro, NC
7:31.69 * Poly- Penn Relays-hs(champ) 4/30/11 Philadelphia, Pa
7:32.06n Green Hope, Cary, NC
NB Natls(R3)(2) 6/16/18 Greensboro
7:32.89 Auburn, Wa
Adidas Classic(R4) 6/14/02 Raleigh, NC
7:33.0+ Jackson, Cambria Heights, NY
Catholic Coaches Relays-spec 6/7/66 Jamaica (7:35.6y)
n+ Boys, Brooklyn, NY
Catholic Coaches Relays-spec(2) 6/7/66 Jamaica (7:35.6y)
7:33.48 * Central Bucks South, Warrington, Pa
State-3A 5/23/09 Shippensburg [Tom Mallon 1:49.0]
7:34.1 * York, Elmhurst, Il
Wanner Knights Invt 4/28/00 Mt Prospect
7:34.45n Lawrence Central, Indianapolis, In
NB Natls(3) 6/17/11 Greensboro, NC
7:34.67 Christian Brothers Academy, Lincroft, NJ
NB Natls(R2) 6/15/12 Greensboro, NC
7:34.8 * York, Elmhurst, Il
vs Proviso West 5/7/85 Elmhurst
7:35.06 Great Oak, Temecula, Ca
NB Natls(R2) 6/18/16 Greensboro, NC
7:35.10n Westfield, Chantilly, Va
NB Natls(R2)(2) 6/15/12 Greensboro, NC
7:35.15 Syosset, NY
NOC Natl HS 6/17/05 Greensboro, NC
7:35.33 South Lakes, Reston, Va
Adidas Classic(R3) 6/15/01 Raleigh, NC
7:35.4+ * Thornton, Harvey, Il
State 5/29/76 Charleston (7:38.0y)
7:35.43n East Greenwich, RI
NB Natls(R3)(3) 6/16/18 Greensboro, NC
7:35.65n Shaker, Latham, NY
NB Natls(4) 6/17/11 Greensboro, NC
7:35.68 Hamden, Ct
New Balance Natls(R2) 6/18/10 Greensboro, NC
7:35.7n+ * Lyons Township, LaGrange, Il
State(2) 5/29/76 Charleston (7:38.3y)
7:35.86n Warwick Valley, Warwick, NY
New Balance Natls(R2)(2) 6/18/10 Greensboro, NC
7:35.87n St Benedicts Prep, Newark, NJ
NB Natls(R3)(4) 6/16/18 Greensboro, NC