Pre-1945 state roads 1-20

One useful source is a 1939 list published by the SRD. I had previously taken notes on all the laws, but this combines them in one handy booklet.

Note that many of the legislatively-defined routes were never built or never acquired by the state. This is especially true of higher numbers.

#	year	from	to	via (post-1945)
1	1923	Alabama	Jacksonville	10 Alabama to Pensacola 10A through Pensacola 10 Pensacola to Quincy 12 Quincy to Havana 12 around Havana (now 159) 63 Havana to Tallahassee 10 Tallahassee to Jacksonville
	branch from Pensacola to Flomaton became 7 in 1925
1-A	1927	Pensacola	Escambia Bay bridge	291
	to be used as a detour for SR 1 during construction missing from the 1939 list (it's not clear if the law intended for it to be a permanent state road) but appears on maps
1-Alt.	1939	1 at Gadsden and 17th, Pensacola (note that 1 cut diagonally across Andalusia Square)	1 at O and Cervantes, Pensacola	30 on 17th Street Gregory Street (now partly 30) 292 on O Street
1-B	1939	1 at Elmira Street, Milton	Canal Street at Milton town limits	Elmira Street Oak Street Canal Street (now partly 191)
	former alignment of 1, at least on Canal Street
2	1923	Georgia	Fort Myers	25 Georgia to Leesburg 44 Leesburg to Eustis 19 Eustis to Mount Dora 500 Mount Dora to Kissimmee 600 Kissimmee to Haines City 544 Haines City to Winter Haven 555 Winter Haven to Bartow 35 Bartow to Arcadia 31 Arcadia to Olga 80 Olga to Fort Myers
2	1923	Leesburg	Lakeland	25 Leesburg to Okahumpka 33 Okahumpka to Lakeland
2	1925	Silver Lake Forks	Mount Dora	500
2	1931	Coleman	Leesburg	468 Coleman to Bamboo 50 Bamboo to Leesburg
2	1931	Dade City	Leesburg	unbuilt Dade City via Clay Sink to Linden 50 Linden to Mabel county roads Mabel to Center Hill (now partly 478) 48 Center Hill to Okahumpka 33/25 Okahumpka to Leesburg
2	1931	Belleview	Rerdell	35
	defined to follow the west side of the railroad (now partly 475) from Coleman to Bushnell, but maps show 2 on current 35 via Sumterville
2	1931	Coleman	Lakeland	35 Coleman to Sumterville 471 Sumterville to Socrum 35 Socrum to Lakeland
	Sumterville to Webster was defined in 1927 as 70
2	1935	Lakeland	Bartow	35
	numbered 124 from 1927 to 1935
2-A	1939	2 south of Gainesville	2 north of Gainesville	329 south of Gainesville 20 north of Gainesville
	north portion is probably old 2
3	1923	Georgia	Orlando	5 Georgia to Jacksonville 211 Jacksonville to north of Orange Park 15 north of Orange Park to Orlando
3-A	1935	3 in Maitland	Orange-Osceola County line	527
	former alignment of 2 and 3 only defined from Winter Park to Orlando until 1939
4	1923	Georgia	Miami	15 Georgia to Jacksonville 5 Jacksonville to Miami 815 in Miami
4-A	1925	Miami	Key West	5
5	1923	High Springs	Fort Myers	45 High Springs to Tampa 43 Tampa to Palmetto 45 Palmetto to Fort Myers
5	1931	Dade City	Denham	52 Dade City to San Antonio 577 San Antonio to Wesley Chapel 54 Wesley Chapel to Denham
5-A	1925	High Springs	Perry	20
	Perry to Branford was defined as 29 in 1923
5-S.E.	1939	Crystal River	West Palm Beach	44 Crystal River to Inverness 45 Inverness to Floral City 39 Floral City to Nobleton Croom Rital Road Nobleton to Rital 700 Rital to Trilby 35 Trilby to Fort Meade 700 Fort Meade to Frostproof 17 Frostproof to De Soto City 66 De Soto City to Okeechobee (now 700) 710 Okeechobee to West Palm Beach
	similar idea as present 700, providing a diagonal across the peninsula completely followed other state roads: 22-5-264-23-34-2-30-8-59-29-117
6	1923	Alabama	Port St. Joe	75/73 Alabama to Marianna 71 Marianna to Port St. Joe
	extended to Apalachicola along 10 until 1925
7	1925	Pensacola	Alabama	95
	7 was not defined in 1923, but the route was part of 1
8	1923	Haines City	Fort Pierce	17 Haines City to Childs 70 Childs to Fort Pierce
8-A	1939	Leesburg	Clewiston	25
9	1923	Georgia	35 near Shady Grove	53 Georgia to Madison 14 Madison to Shady Grove
10	1923	Georgia	Pensacola	61 Georgia to Tallahassee 363 Tallahassee to Wakulla 365 Wakulla to Shadeville 61 Shadeville to Medart 375 Medart to Sopchoppy 377 Sopchoppy to northeast of Lanark 30 northeast of Lanark to Laguna Beach 79 Laguna Beach to Ebro 20 Ebro to Niceville 85 Niceville to Valparaiso 397 Valparaiso to Eglin AFB 85 Eglin AFB to Fort Walton Beach 30 Fort Walton Beach to Navarre 87 Navarre to Milton 10 Milton to Pensacola
	went only to Eastpoint until 1925 (replaced 6 from Apalachicola to Port St. Joe)
10	1925	Wakulla	northeast of Lanark	363 Wakulla to southeast of Wakulla 30 southeast of Wakulla to northeast of Lanark (now partly 363; portion from St. Marks to Panacea unbuilt)
	went Woodville-Newport-St. Marks until 1931; Wakulla-St. Marks cutoff bypassing Newport defined in 1927 as 101 and became part of 10 in 1931
10	1931	Crawfordville	Arran	368
	also part of 129
10	1931	southeast of Wakulla	Waukeenah	30 southeast of Wakulla to Newport 59 Newport to Wacissa 259 Wacissa to Waukeenah
10-A	1935	1 east of Tallahassee	10 south of Tallahassee	265
10-A	1937	Perry	Tallahassee	30 Perry to Cabbage Grove (Perry-Hampton Springs was not part of 30 in 1945) unbuilt Cabbage Grove to Cody 259 Cody to Tallahassee
10-B	1937	10 at Everitt Avenue	10 at Cherry Street	30A
10-B	1939	10 near St. Teresa	10 near Metcalf Point; 10 near McIntyre	370 (branch to St. Teresa unbuilt)
10-C	1937	10 in St. Andrews	20 in Panama City	30A
10-D	1939	10-B	Panama City Municipal Docks	unbuilt
11	1923	Georgia	Capps	57
	ended at Monticello until 1925
12	1923	Georgia	Eastpoint	65 Georgia to Quincy 12 Quincy to Bristol 67 Bristol to Woods 379 Woods to Sumatra 65 Sumatra to Eastpoint
	defined in 1923 from Bristol to Georgia via Telogia, Hosford, and Quincy; rerouted in 1925 via Greensboro and extended to Eastpoint; maps show that it continued to serve Telogia and Hosford (turning south from Greensboro) until 1933, when 135 and 136 were extended past Telogia and 12 was placed on a more direct route through Bristol
13	1923	Cedar Key	Atlantic Ocean at Fernandina	24 Cedar Key to Waldo 200 Waldo to Fernandina
	ended at Baldwin until 1925, Yulee until 1927
14	1923	500 near Old Town	St. Augustine	26 Old Town to Gainesville 20 Gainesville to Palatka 206 Palatka to Hastings 13 Hastings to Spuds 207 Spuds to St. Augustine
	went from Gainesville to Hastings in 1923; extended west to Old Town in 1925 and east to Crescent Beach in 1931; rerouted to St. Augustine in 1935 (replacing part of 189, which was defined in 1931 but had been the alignment of 4; old route to Crescent Beach became 14-A)
14-A	1935	Deep Creek	Crescent Beach	206
	defined as part of 14 in 1931 another 14-A shows up on a 1930s Alachua County map but does not seem to have been defined by law
15	1923	10 southeast of Wakulla	St. Petersburg	30 southeast of Wakulla to Newport unbuilt Newport to Adams Beach 361 Adams Beach to near Big Grassy Island unbuilt near Big Grassy Island to Inglis 55 Inglis to Holiday 595 Holiday to St. Petersburg
	went from Brooksville to St. Petersburg in 1923; north end changed to Newport in 1925 (replacing part of 16; branch to Brooksville was kept) and extended to 10 in 1935
15	1923	5 north of Brooksville	Weeki Wachee	45A north of Brooksville 50 Brooksville to Weeki Wachee
	extended north from Brooksville in 1935
15	1937	Chiefland	Inglis	55
	formerly part of 81 (Chiefland-Lebanon Station, 1927) and 81-A (Lebanon Station-Inglis, 1931)
15-A	1935	Wakulla	Panacea; Perry	267 Wakulla to Newport Newport Road Newport to St. Marks 30 St. Marks to Panacea (unbuilt) 30 Newport to Wacissa River (eventually built a bit to the south, between 15 and 15-A) unbuilt Wacissa River to Hampton Springs 30 Hampton Springs to Perry (not part of 30 in 1945)
	only defined from Wakulla to Newport in 1935; extensions both ways from Newport added in 1937 (most of Newport-Panacea was already part of 10)
16	1923	Ocala	Red Level	40 Ocala to Juliette 45 Juliette to Dunnellon 488 Dunnellon to Red Level
	continued south to 15 at Aripeka in 1923; cut back to Crystal River in 1925 and relocated to Red Level by 1939 (absorbing 168, Dunnellon to Red Level, defined 1931)
16-A	1931	Juliette	Yankeetown	unbuilt Juliette to west of Dunnellon 40 west of Dunnellon to Yankeetown
17	1923	Deer Park	Clearwater	unbuilt Deer Park to Haines City 600 Haines City to Tampa 580 Tampa to Bridgeport 590 Bridgeport to Clearwater
	extended east from Haines City to Deer Park in 1927; east end may have been relocated to Holopaw in 1943 (need to look up chapter 21897)
18	1923	Bradenton	Childs	Manatee Avenue (now 64)/Palma Sola Boulevard/684 (also part of 18-A) Bradenton to Bradenton Beach 780 Bradenton Beach to Old Myakka (now 789 west of Sarasota) Clay Gully Road Old Myakka to Pine Level 70 Pine Level to Childs
	Sarasota to Bradenton added in 1935
18-A	1925	Anna Maria	Pine Level	684 Anna Maria to Bradenton 70 Bradenton to Pine Level
	extended west from Bradenton in 1935 also defined to run south from Bradenton Beach to the Manatee-Sarasota County line, but this was also part of 18 and does not appear on maps as 18-A
19 was renumbered 500 in 1939 (due to confusion with US 19) but 19-A remained
19-A	1937	500 northwest of Perry	500 south of Perry	unbuilt northwest of Perry 55 through and south of Perry (also part of 35)
20	1923	6 northeast of Cottondale	Harrison at Beach, Panama City	75
	originally went only south from Cottondale; extended to 6 in 1925
20-A	1941	20 at 11th Street in Panama City	10 in St. Andrews	22 (now 28)
20-B	1937	Nixon	500 at Sugar Creek	Scotts Ferry Road/CCC Road 16 Nixon to Little Cypress Creek unbuilt Little Cypress Creek to Sugar Creek
What was legislated as 20-C in 1937 was instead numbered as part of 10-C by the SRD (the part east of State Convict Camp 37)
20-D	1939	20 in Panama City	10-D	Beach Drive, Cherry Street, unbuilt