First and Last frosts shown below are 'average' and vary year to year. There are lots of tables on the web with different dates, this is just one example. Within each town or city there will be differences due to microclimates. Use the dates as guidelines. For example, I live outside of Baltimore MD, which is listed with a last frost date of March 26th. Balitmore is always at least 10 degrees warmer than my yard, so I use April 22nd as the last frost date for my gardens.

Mobile AL 272 Feb. 27 Nov. 26
Juneau AK 133 16-May Sept. 26
Phoenix AZ 308 Feb. 5 Dec. 15
Tucson AZ 273 Feb. 28 Nov. 29
Pine Bluff AR 234 Mar. 19 Nov. 8
Eureka CA 324 Jan. 30 Dec. 15
Sacramento CA 289 Feb. 14 Dec. 1
San Francisco CA * * *
Denver CO 157 3-May Oct. 8
Hartford CT 167 Apr. 25 Oct. 10
Wilmington DE 198 Apr. 13 Oct. 29
Miami FL * * *
Tampa FL 338 Jan. 28 Jan. 3
Athens GA 224 Mar. 28 Nov. 8
Savannah GA 250 Mar. 10 Nov. 15
Boise ID 153 8-May Oct. 9
Chicago IL 187 Apr. 22 Oct. 26
Springfield IL 185 Apr. 17 Oct. 19
Indianapolis IN 180 Apr. 22 Oct. 20
South Bend IN 169 1-May Oct. 18
Atlantic IA 141 9-May Sept. 28
Cedar Rapids IA 161 Apr. 29 Oct. 7
Topeka KS 175 Apr. 21 Oct. 14
Lexington KY 190 Apr. 17 Oct. 25
Monroe LA 242 Mar. 9 Nov. 7
New Orleans LA 288 Feb. 20 Dec. 5
Portland ME 143 10-May Sept. 30
Baltimore MD 231 Mar. 26 Nov. 13
Worcester MA 172 Apr. 27 Oct. 17
Lansing MI 140 13-May Sept. 30
Marquette MI 159 12-May Oct. 19
Duluth MN 122 21-May Sept. 21
Willmar MN 152 4-May Oct. 4
Columbus MS 215 Mar. 27 Oct. 29
Vicksburg MS 250 Mar. 13 Nov. 18
Jefferson City MO 173 Apr. 26 Oct. 16
Fort Peck MT 146 5-May Sept. 28
Helena MT 122 18-May Sept. 18
Blair NE 165 Apr. 27 Oct. 10
North Platte NE 136 11-May Sept. 24
Las Vegas NV 259 Mar. 7 Nov. 21
Concord NH 121 23-May Sept. 22
Newark NJ 219 Apr. 4 Nov. 10
Carlsbad NM 223 Mar. 29 Nov. 7
Los Alamos NM 157 8-May Oct. 13
Albany NY 144 7-May Sept. 29
Syracuse NY 170 Apr. 28 Oct. 16
Fayetteville NC 212 Apr. 2 Oct. 31
Bismarck ND 129 14-May Sept. 20
Akron OH 168 3-May Oct. 18
Cincinnati OH 195 Apr. 14 Oct. 27
Lawton OK 217 Apr. 1 Nov. 5
Tulsa OK 218 Mar. 30 Nov. 4
Pendleton OR 188 Apr. 15 Oct. 21
Portland OR 217 Apr. 3 Nov. 7
Carlisle PA 182 Apr. 20 Oct. 20
Williamsport PA 168 Apr. 29 Oct. 15
Kingston RI 144 8-May Sept. 30
Charleston SC 253 Mar. 11 Nov. 20
Columbia SC 211 Apr. 4 Nov. 2
Rapid City SD 145 7-May Sept. 29
Memphis TN 228 Mar. 23 Nov. 7
Nashville TN 207 Apr. 5 Oct. 29
Amarillo TX 197 Apr. 14 Oct. 29
Denton TX 231 Mar. 25 Nov. 12
San Antonio TX 265 Mar. 3 Nov. 24
Cedar City UT 134 20-May Oct. 2
Spanish Fork UT 156 8-May Oct. 12
Burlington VT 142 11-May Oct. 1
Norfolk VA 239 Mar. 23 Nov. 17
Richmond VA 198 Apr. 10 Oct. 26
Seattle WA 232 Mar. 24 Nov. 11
Spokane WA 153 4-May Oct. 5
Parkersburg WV 175 Apr. 25 Oct. 18
Green Bay WI 143 12-May Oct. 2
Janesville WI 164 Apr. 28 Oct. 10
Casper WY 123 22-May Sept. 22
*Frosts are rare.